CHAPTER 5: REALITY
From Great Issues in Philosophy, by James Fieser
Home: https://storage.googleapis.com/jfieser/120/Index.html
© 2008, updated 6/1/2025, CC BY-NC-ND 4.0
CONTENTS
Subjective Idealism
Absolute Idealism
Panpsychism
B. Time
Does Time Flow: Dynamic Theory vs. Static Theory
Time Travel
The Ship of Theseus and Identity over Time
C. Abstract Objects
Realism
Anti-Realism: Nominalism and Conceptualism
Fictional Objects
Substance: Substratum Theory vs. Bundle Theory
D. Criticisms of Metaphysics
Kant: The Human Mind cannot Access Metaphysical Reality
Logical Positivism: Metaphysical Statements are Meaningless
Scientism: Reality is the Domain of Science, not Metaphysics
References
Study Questions
In 1666, English philosopher Margaret Cavendish published a work of utopian fiction titled Blazing Worlds, which describes a parallel universe that the story's heroine accesses through a portal at the north pole. This new world has completely different celestial constellations, and its earth-like planet contains species of people shaped like animals, including "some Ant-men, some Geese-men, some Spider-men, some Lice-men, some Fox-men, some Ape-men". The planet's Emperor falls in love with the heroine, they marry, and he gives her "absolute power to rule and govern all that World" as she pleases. She subsequently uses her authority to advance science and assigns the people occupations that best suit their natures and, thus, fox-men become politicians and parrot-men become orators. Eventually she sends an army of the aliens back to earth to help fight England's enemies.
Cavendish's book was one of the first works of science fiction written by a woman, and it also stands out as perhaps the first to involve a parallel universe. Fictional works about parallel universes and multiverses are commonplace now, and in recent decades physicists have begun to take seriously the idea that our universe may be only one of an infinite number. They speculate that some of these parallel worlds closely resemble ours, and others are wildly different with their own dimensions and laws of nature. But even before physicists entertained the idea of a multiverse, the philosopher David Lewis suggested that there exists an infinite number of possible worlds where, again, some resemble our own, and others do not. Lewis suggested this as a way of explaining our ordinary conviction that events in this world could have been different than the way they are. For example, while I in fact purchased a white car, I could instead have purchased a red one. For Lewis, in some possible world I did purchase a red one. Thus, when I say that "I could have purchased a red car" my statement is about that specific possible world. Lewis believes that these possible worlds exist as concretely as ours does. Some of his critics, though, argue that such worlds do not have concrete existence, but instead have only abstract existence.
Lewis and his critics are engaged in a dispute about the types of entities that exist, which is a question of metaphysics. Metaphysics is the study of the fundamental nature of reality. The origin of the term "metaphysics" is unclear, but it rests on two Greek words: meta (beyond) and phusis (nature). The implication is that metaphysics attempts to describe the reality of the world beyond what science tells us about it, and, as such, it as an investigation of things that exist apart from what is immediately apparent in the physical world around us. Metaphysical questions explored in previous chapters include "Does God exist and, if so, what is his nature?", "Do humans have genuinely free wills or are our actions determined?", "Are our minds physical or non-physical", and "Can my conscious mind survive the death of my body"? These questions are metaphysical since, while they are all reasonable enough to ask, they cannot be settled through purely scientific methods.
In this chapter we will explore other metaphysical issues of reality that involve idealism, time, and abstract objects. We will also look at criticisms of the entire field of metaphysical speculation.
A. IDEALISM
Part of the task of metaphysics is to take an inventory of the kinds of things that exist, and philosophers disagree about how many there are. A traditional classification of metaphysical entities is between two general types, with some subdivisions:
• Monism: one type of thing exists
• Materialism: only matter exists
• Idealism: only spirit-mind exists
• Dualism: two types of things exist (matter and spirit-mind)
As its name implies, monism is the theory that there is only one fundamental type of thing in the universe: maybe it's just matter as materialism holds, or maybe it's just spirit-mind as idealism holds. Dualism, by contrast, is the theory that there are two types of things, namely matter and spirit-mind. We've discussed dualism and materialism in other chapters. Of the four "isms", though, idealism is the most counterintuitive, and in what follows we will explore different versions of it. The term "idealism" is based on the word "idea", insofar as, according to many traditional philosophers, ideas are spiritual-mental in nature. On this view, while it might seem as though there are material objects, this is just a misunderstanding or even an illusion. The reality is that everything we perceive is spiritual-mental in its nature, rather than material.
Subjective Idealism
A popular plotline in science fiction films involves people who are trapped in a virtual reality, completely unaware that what their perceiving is not a reflection of events in the physical world. In the Matrix, for example, the hero believes that he works at a job as a computer programmer, lives in a small apartment, and is a hacker in his spare time. In reality, though, his physical body is submerged in a container of goo where he is kept alive by tubes and wires. A computer cable is attached to the back of his neck, which, unknown to him, connects him to a virtual reality with which he interacts.
Life within the Matrix is very much like the world as envisioned by the theory of subjective idealism, which, in its most general form, is that the world consists only of individual minds and their contents. The leading proponent of this view is Irish philosopher George Berkeley (1685-1753). According to him, there simply is no three-dimensional physical world. All that exists is a vast number of finite spirit-minds that are connected to God. Much like the Matrix, God injects perceptions of things like rocks and trees into our spirit-minds, thereby creating a virtual reality with which we all can interact. When I have a conversation with you, your physical body that appears before me is only an avatar that God has selected for you, and the sound of your voice is also part of that avatar. The back and forth interaction between our avatars is so convincing and seamless, that we simply assume that our minds are implanted within actual physical bodies. Nevertheless, all that truly exists is our human spirit-minds connected to God.
Berkeley's main argument for his subjective idealism is that the existence of a table or house is necessarily tied to our perception of it. In his words, "what is said of the absolute existence of unthinking things [like tables], without any relation to their being perceived, that is to me perfectly unintelligible" (Principles, 3). When I look at a table, I do not perceive any actual three-dimensional physical thing, but instead I am only receiving perceptual data through my senses. In fact, the only things that my mind has direct access to are perceptual data and my ideas about them. It is completely beyond my experience to imagine a table existing by itself as a three-dimensional thing, independently of my perceptual data about it. It doesn't need to be me specifically doing the perceiving, but, for us to say that a table exists, some mind needs to be having the perception. Thus, for Berkeley, the concept of an unperceived material thing is inherently contradictory. Not only is there no physical table, but I myself have no physical body: I am simply a mind that is being fed perceptual data of a table and my body. We might now ask: if my mental images of a table and my body do not come from genuine physical objects, where then do those mental images come from? His answer is that God injects that perceptual data into our minds, thereby creating a virtual reality. This, he believes, is a much better explanation than to say that we get those images from mysterious three-dimensional things that we can never directly experience.
Berkeley sums up his attack on material objects with the motto "to be is to be perceived", that is, a thing's existence reduces to the act of perceiving it. In its simplest form, his argument is this:
1. If a material thing exists, then we must have some direct perception of that thing.
2. We have no direct perception of material things, since we only directly perceive perceptual data.
3. Therefore, material things do not exist.
Does this argument work? Premise two is reasonable enough, namely, that "We have no direct perception of material things, since we only directly perceive perceptual data." There is a long-standing assumption in modern philosophy that a barrier exists between our minds and external objects: my only access to the table in front of me is through perceptual data. A few philosophers have attempted to argue to the contrary that when I view a table, I am directly seeing the actual table itself, and not a mere perceptual copy of it. But this is a difficult case to make considering that my perceptual image of a table is completely dependent upon the limited machinery of my sense organs. Thus, premise two stands.
Premise one, though, is less convincing, namely, that "If a material thing exists, then we must have some direct perception of that thing." Just because we are incapable of directly perceiving physical objects doesn't mean that nothing physical is there. There is an alternative to directly perceiving physical things, which is that we "indirectly" perceive them through our sense organs. The actual physical table itself may look nothing like what my sense organs tell me about it, but at least I get enough data about the table to construct a plausible representation of at least part of the table. In short, premise one fails for overlooking the reasonable explanation that we perceive three dimensional physical objects indirectly.
When Berkeley first proposed his theory, it seemed too bizarre to be credible, and it is only in recent decades through our growing fascination with virtual reality that we might seriously consider subjective idealism as a possible account of the universe as we know it. There is something called the "simulation hypothesis" proposed by contemporary philosopher Nick Bostrom (b. 1973) which states that the odds are good that we are already living in a virtual reality created by our ancestors. As the theory goes, let's assume, first, that the technology is possible to create conscious minds within a computer simulation, and, second, that an advanced civilization had the desire to do so. This means, then, that by now our predecessors would likely have produce billions of simulated worlds containing billions of conscious minds, which would vastly outnumber all flesh and blood conscious minds that have ever existed. Thus, the odds are good that your conscious mind is a simulated one, rather than a flesh and blood one. There are major assumptions in Bostrom's argument, and the failure of any one of them makes his conclusion less compelling. Still, with every new advancement in virtual reality technology, we can't help but to take his simulation hypothesis seriously.
The most disturbing aspect of subjective idealism is that, even if we reject it, we can't disprove it. The reason, as indicated in premise two in the above argument, is that we are blocked from direct access to the external world, and so we can never know with absolute certainty what is feeding us perceptual data. Maybe it's physical objects, maybe it's Berkeley's God, maybe it's Bostrom's computer simulation. We simply don't know for sure and, so, we will forever be haunted by Berkeley's challenge that "to be is to be perceived".
Absolute Idealism
While Berkeley's theory of subjective idealism never took hold among traditional philosophers, another type of idealism has been popular since philosophy's earliest days. Absolute idealism is the view that Absolute Mind, or eternal consciousness, is all that is real, and each finite mind is only a part of it. Absolute idealism emphasizes the collective nature of consciousness, a concept which is prevalent in science fiction under the term "group mind" or "hive mind". A famous example of this is Olaf Stapledon's The Star Maker (1937), which describes the journey of a man who is pulled into outer space and assimilated into a communal consciousness of aliens. This communal mind then goes on to connect with increasingly larger conscious entities, including the minds of stars and galaxies, which in turn all merge into the embryonic mind of our particular universe. Pushing further, the cosmic mind then connects with the "Star Maker", the absolute mind and creator of all universes. The Star Maker himself began as an embryonic mind, but slowly matured by fashioning one universe after another. As each of these created universes reached "some unique achievement of awareness and expression", they became "the instrument by which the Star Maker himself, cosmos by cosmos, woke into keener [conscious] lucidity."
Stapledon was a follower of German philosopher Georg Wilhelm Friedrich Hegel (1770-1831), the most important proponent of the theory of absolute idealism, and, Stapledon's science fiction is modeled after Hegel's philosophy. In traditional theology, God is an unchanging being who, since eternity past, is all-powerful, all-knowing, and all-good. Not so for Hegel. God was once a child but has grown up over time. To bring about his growth, God transformed himself into physical matter, which includes not only the world around us but we human beings ourselves. We humans have improved over time by expanding our knowledge and creating societies that become increasingly sophisticated. Thus, through our human and social development, God himself has become more advanced, ultimately achieving complete self-awareness, and thereby becoming the Absolute Mind of the cosmos.
According to Hegel, God's developmental process involves three stages of conflict-and-resolution that have repeatedly occurred throughout time: (1) a thesis, (2) an antithesis opposing it, and (3) a synthesis that emerges as the outcome of the tension between the first two. This synthesis then becomes a new thesis which in turn is opposed by a new antithesis, and the pattern continues. Hegel explains this process with the metaphor of a growing plant: What is the real plant, you may ask. Well, it is a bud (thesis). But wait, the bud has now become a flower, which refutes the suggestion that the plant is a bud (antithesis). But look again, the flower has become fruit, refuting even this (synthesis). So, what is the plant? The answer is that its reality progressively unfolds: it is an organic unity that involves the life of the plant as a whole (Phenomenology, Preface). In the same way, Hegel argues, God's reality progressively develops through a series of ideological conflicts within society that, at the time, seem incompatible with each other.
Hegel's theory of absolute idealism is multifaceted, but its core notion is simply that all reality is the absolute mind of God. He summarizes this with the motto "The real is the rational, and the rational is the real" (Philosophy of Right, Preface). That is, mind and reality are not distinct: the outside world is known through reason, and reason is known through the outside world. His principle argument for absolute idealism is that anything we attempt to say about the reality of the world inevitably leads to the conclusion that it is mental-spiritual in nature. More precisely, the argument is this.
(2) That which is intelligible is rational.
(3) The rational is mental (spiritual) in nature.
(4) Therefore, reality is mental (spiritual) in nature
The strategy of the above argument is to link together the three concepts of "intelligibility", "rationality" and "mental". It seems harmless to say that reality is intelligible, since intelligibility is just the mental mechanism by which we scientifically understand things. In Hegel's words, intelligibility is simply "the form in which science is offered to everyone, and is the open road to it made plain for all" (Ibid.). It also seems harmless to say that what is intelligible is rational, since reason is the mental mechanism by which we intelligibly understand things. He writes, "To reach rational knowledge by our intelligence is the just demand of the mind" (Ibid). Finally, it seems harmless to say that the rational is mental in nature, since reasoning is simply a mental activity. The conclusion thus follows that reality is mental in nature, that is, the reality of the total world is the Absolute Mind.
Does this argument succeed? There are two problems with it. First, a skeptic would stop at premise 1 and question whether reality is truly intelligible. We noted earlier the common philosophical conviction that a barrier exists between our minds and the external world. While I certainly have perceptions of things like trees, I do not know what in reality lies behind my perceptions. It could be a physical thing that is just like my perception of the tree, or maybe it's nothing like my perception of it at all. But even if we ignore this skeptical doubt, there is a second and more important problem with this argument that involves premise 2. Again, the premise is, "That which is intelligible is rational." However, there are two different ways we can interpret this premise:
(2a) if an object is intelligible, then that object itself is a rational thing (and is thereby a mental thing).
(2b) if an object is intelligible, then that object can be known to some observer through reason (and is thereby known through the mind).
Interpretation 2a is Hegel's intended meaning, and it indeed leads to idealism. But interpretation 2b does not lead to idealism, and this is the more natural understanding of that premise. That is, according to interpretation 2b, it is only our minds that are endowed with reason, not the objects that we are attempting to understand. Thus, unless we are already inclined towards absolute idealism, there is no good reason to accept interpretation 2a over 2b, and so the argument fails.
While this particular argument for idealism is unsuccessful, this does not necessarily mean that absolute idealism is a false theory. Since I am blocked from directly accessing the external world itself, the possibility is still open that Hegel is correct, and I am just a little piece of a giant cosmic mind.
Panpsychism
Nanobots! They are microscopically small machines with artificial intelligence, and, according to the science fiction TV series Stargate Atlantis, they can swarm together to form people, cities, and even complete planets. If you are a fan of nanobots, there is good news: according to the theory of panpsychism, you yourself are made of something like nanobots. Panpsychism is the view that everything material, however small, has an element of individual consciousness. At first panpsychism may look like absolute idealism. However, Hegel's idealism is about God growing up, from infancy to adulthood, where progressively developing human minds and societies enhance God's mind. Panpsychism, though, is not about God, and in fact some of its leading advocates have been atheists. Rather, it is about how the tiniest physical objects have elementary mental properties which, when combined, make larger and more sophisticated conscious bodies like animals and humans. The theory is monistic, rather than dualistic. For, as we have seen, dualists say that there are two radically different types of things in the universe: (1) three-dimensional material things that are non-mental, and (2) non-three-dimensional spirit-minds that are mental. Panpsychism is different, though, since it says that every existing thing is both material and mental at the same time. For example, in the following, Bertrand Russell describes his particular panpsychist theory, which he calls "neutral monism":
[Neutral monism is] the theory that the material constituting the mental is the same as the material constituting the physical, just like the Post Office directory which gives you people arranged geographically and alphabetically. ["Logical Atomism", 3]
Panpsychism thus attempts to straddle the fence between monistic materialism and monistic idealism, but, with its emphasis on mind, it leans slightly more in the idealist direction.
Defenders of panpsychism do not claim that small particles like atoms have the same types of sophisticated minds that human beings do. According to Gottfried Wilhelm Leibniz, the smallest existing things, which are the size of mathematical points, have the capacity for what he calls "tiny perception", and he describes this as an unconscious mental state like a deep sleep. He argues that it takes a vast number of these tiny perceptions, accumulated together, to rise to the level of a fully conscious experience. Panpsychists have different views about what type of mental events go on within the mini-minds of tiny particles. Leibniz says they can sense their surroundings, like a minuscule motion detector. Arthur Schopenhauer says that they have an inner "will to live", that is, an inner desire or yearning. Water, he says, has an unceasing impulse to rush to the ocean, magnets to point to the north pole, crystals to take regular forms, and even stones to exhibit cohesion and rigidity. According to Schopenhauer, each of these "in its inner nature [is] the same as that which I recognize in myself as will" (The World as Will, 2.1.25).
In spite of how strange the theory of panpsychism sounds, many respectable philosophers and scientist up to the present day have embraced the theory. The main argument for it is this. Let's accept the fact that human consciousness is a function of brain activity. But consciousness is such an odd thing that even our best science is nowhere close to explaining how our physical brains produce it, or at what point in the evolutionary development of animals it could have appeared. The reason is that raw matter, as we usually understand it, does not seem to be the kind of thing that can be assembled together from tiny bits to create a larger thing with conscious awareness. We must thus reject this usual understanding of matter and instead accept the view that all material things have elementary aspects of consciousness within them, or "tiny perceptions" using Leibniz's terminology. More formally, the argument is this:
(1) Small pieces of matter either have elementary consciousness or lack it.
(2) If small pieces of matter lack elementary consciousness, then they cannot be assembled together to form a fully conscious thing.
(3) But small pieces of matter can be assembled together to form a fully conscious thing.
(4) Therefore, small pieces of matter have elementary consciousness.
Of the three mind-based theories that we've looked at so far, panpscyhism is the most compelling since it arises from a scientific need. It is a way to explain how the atoms that once swirled around in galactic space eventually clumped together into the human brain and became conscious. The explanation is that each of those atoms had elementary consciousness all along.
Let's now look at two criticisms of panpscyhism, the first of which is called the "combination problem": individual mental experiences cannot self-compound into larger ones. This is a direct rejection of premise 3 above. Let's suppose for the moment that each atom has some elementary consciousness. How, then, do all of these tiny conscious experiences mix together to form one larger and more sophisticated conscious experiences? William James, who first put forward this criticism, gives this example. "Take a sentence of a dozen words, and take twelve men and tell to each [man] one word. Then stand the men in a row or jam them in a bunch, and let each think of his word as intently as he will; nowhere will there be a consciousness of the whole sentence" [Principles, 6.4]. The point is that the consciousness of an atom would be a private experience that is isolated to that specific atom, and it cannot simply mix with the consciousness of surrounding atoms to form a larger collective mind.
While the combination problem has been a major challenge to panpsychism, it is not insurmountable, and it comes down to the question of interface: how can you get two or more private minds to connect and share mental experiences? With James's example, the low-tech solution is for a thirteenth man to simply ask each of the other twelve what his word is, and the thirteenth can be conscious of the whole sentence. The interface here is verbal human communication. Let's push this a step further and consider a biological interface that scientists have observed: conjoined twins connected at the head from birth can hear each other's thoughts. Similarly, if all twelve of these men were from birth joined at the head to the thirteenth, then the thirteenth could be conscious of the whole sentence. Pushing this even further, a high-tech interface would be to wire the twelve men's brains together, with one master brain and twelve slave brains (to borrow an expression from computer science). This is not just science fiction, for, in an experiment already conducted, monkeys whose brains have been connected to a computer can perform complex tasks better as a group than they can individually. If such a mind-to-mind interface is possible with sophisticated human and animal minds, it is reasonable to assume that something similar could happen at a much tinier level with clusters of molecules connected in a master-slave interface. Thus, maybe the tiny conscious experiences of atoms can mix together to form one larger conscious experience in human and animal minds.
The second criticism of panpsychism is that it commits what logicians call the fallacy of division, namely the assumption that the parts of a thing have the properties of the whole. For example, your mobile phone has the property of displaying light, therefore, you fallaciously conclude, its on-off switch must also have the property of displaying light. It's true that each of the phone's pixels can display light, but the on-off switch and most other components do not. Similarly with panpsychism, while it may be true that subcomponents of your brain have consciousness, perhaps even very tiny clusters of neurons, it is wrong to conclude that a hair follicle, an ankle bone, or a molecule of iron in your blood also has consciousness. In recent times, the drive to extend consciousness to everything is not so much based on science, but on wishful thinking, and the hope of filling a gap in our knowledge about where human consciousness comes from. While the theory of panpsychism does offer a solution, it currently is a theory that's more at the level of science fiction than science fact. Panpsychism is an interesting theory and has nice ethical implications about the respect that we should show to all things, organic and inorganic. But the evidence for the theory isn't there yet and may never be.
Thus, as of yet there is no proof that panpsychism is true, since we do not have any direct evidence that atoms have tiny conscious experiences. However, like subjective idealism and absolute idealism, panpsychism is at least a theoretically plausible explanation of reality.
B. TIME
We are trapped on the timeline, like a bug crawling along a flat surface, with no opportunity to rise above it, glance around, and see if there is more to time than what we experience. One thing we would like to know about time is its structure, and there are different possibilities for how the timeline might be laid out:
• Bounded or unbounded: whether time has a beginning or an end.
• Continuous or discrete: whether points in time are infinitely small or finite particles.
• Linear or closed loop: whether time circles back on itself and repeats.
• Branching or non-branching: whether the timeline splits off creating new lines.
• Single or multiple: whether there are parallel timelines.
Does Time Flow: Dynamic Theory vs. Static Theory
We commonly speak of time as flowing like a river, with each event continually moving from the present into the past. In 1922, Albert Einstein met with philosopher Henri Bergson in Paris to publicly debate just this point: does time actually flow? Bergson held the common-sense view that the flow of time is a genuine feature of time itself, which we directly experience in our human lives. Einstein disagreed, arguing that physics shows that actual time does not flow at all: time is like a bundle of photographs of every event in the universe, from the Big Bang to the Big Freeze, all lined up in an unchanging box titled "space-time". My personal experience of the flow of time is relative, and it depends upon my specific motions as I ruffle through the box. But the box remains intact, with all its pictures permanently fixed. Accordingly, Einstein concludes, the flow of time as we experience it is an illusion, and "the philosopher's [concept of] time does not exist". Their debate was a contest between time as perceived by living humans vs. time as embedded in the physical universe itself. Bergson accused Einstein of building a bad metaphysics of time on top of physics, while Einstein faulted Bergson for not understanding his theory of relativity. The debate between the two great thinkers was not a new one, and the same dispute continues today under the names "dynamic time theory" (Bergson's view, also called "A-Theory") and "static time theory" (Einstein's view, also called B-theory). Let's consider each in more detail.
Dynamic time theory is the view that "flow" or "passage" is central to the nature of time, and it occurs in reality independently of our minds. Time moves in such a way that present events progressively retreat into the past and future events progressively advance towards the present. There are different versions of dynamic time theory, and the three main ones are these:
• Presentism: only the present is real, and the present loses its reality when it moves into the past.
• Growing Past Theory: both the present and past are real, and the past continually grows as each new present moment recedes into the past.
• Moving Spotlight Theory: the past, present and future are all real, and the present moves along the spectrum from earlier times to later times, like a spotlight across a field.
The three theories differ about the reality that they give to the past and future. But all three assume that there is something metaphysically unique or privileged about the present which differentiates it from the past and future. The most intuitive of the three, though, is the moving spotlight theory, which is how we will represent and discuss the dynamic time theory here.
By contrast, static time theory is the view that time itself does not flow or unfold, but instead is a fixed set of events. An early defender of this view is the ancient Greek philosopher Parmenides, who famously argued that reality is timeless and unchanging, despite how things appear to us. The current version of static time theory comes from modern physics and the concept of the "block universe", where all of space-time is represented as an unchanging four-dimensional block. This is analogous to the giant box described earlier that contains photos of every event within the universe's history. On this view, past, present and future events all exist in the same way, and the present has no special status. Using another analogy, within space, my present location has no special metaphysical status over London, Tokyo or anywhere else. Similarly, within time, this present moment has no special metaphysical status over any event in the year 1776 or 2776. They all co-exist equally within the block universe, and what we conceive of as the "present" is only an invention of our biological minds and how it evolved. That is, we first perceive nearby space-time events through our sense organs, and then mentally assemble that sensory data into a flowing narrative. We experience these events as though they are coming into being, but the reality is that all of these events already exist within the space-time block universe. Thus, the "flow" of time that our minds create is an illusion that hides the true nature of all events within space-time as parts of an unchanging block. To be clear, when claiming that time is an illusion, static time theorists are not denying that we experience time flow. Rather, they are only saying that our experience of time flow is a fabrication of our animal brains that does not match with the static reality of the block universe. Defenders of static time theory sometimes call this illusion "the myth of passage".
Between dynamic and static time theories, then, is one better than the other? The main advantage of static time theory is that it is supported by our best science. If we are interested in knowing how the physical world works, science is typically our most reliable source. But critics of static theory see a problem: it is not clear how a series of frozen space-time events can generate the conscious illusion of time flow within a person's mind. Let's assume that there is indeed a block universe, let's also assume that human consciousness is the result of brain activity. Thus, my brain, at its various ages, is spread throughout a sequence of permanent events within the block universe. According to critics, it is not clear how, in this fractured and frozen condition, my brain can generate even the illusion of time flow. This is sometimes called "the hard problem of time" (paralleling "the hard problem of consciousness" in the philosophy of mind). The problem is indeed a difficult and multifaceted one. Part of the challenge involves biology, and neurologists are exploring different theories of how the brain processes time.
Another part of the problem is a logical one: how can consciousness itself exist without moving through time? Something needs to move for the brain to even have the illusion of time flow. It seems that we need something like dynamic time theory's moving spotlight of presentness to shine along the block universe to give my brain that experience. Here, though, is a possible solution to this criticism. Consider first these five ways that, within the framework of dynamic time theory, the spotlight might work, each of which is compatible with my current experience of time flow and presentness:
1. Single forward sweep: the spotlight of presentness makes one sweep across the block universe from the Big Bang to the Big Freeze; right now I am somewhere on that sweep.
2. Single bi-directional sweep: this is like option 1, but there is a return sweep where the arrow of time reverses direction; right now I am somewhere on the forward sweep, and on the return sweep I will relive my life in reverse.
3. Consecutive bi-directional sweeps: this is the same as 2, but the spotlight continually sweeps back and forth; right now I am somewhere on a forward sweep, then will relive my life in reverse, then forward, then reverse, and so on forever.
4. Concurrent bi-directional sweeps: this is the same as 3, but many spotlights continually sweep back and forth; right now I am somewhere on a forward sweep of one spotlight, but several of my duplicate selves are on their forward and reverse sweeps of their respective spotlights.
5. Block floodlight: the spotlight of presentness does not make any sweeps, but instead illuminates the entire block universe; right now I am permanently experiencing the presentness of one single event; future and past versions of me are each permanently experiencing the presentness of their own single event.
Scenario 1 is what the dynamic time spotlight theorist presumes to be the case. But scenarios 2-4 are equally consistent with my current experience of time flow. That is, based on my own private experience of the present moment, I could be living in any of these first four scenarios.
What is unique about scenarios 2-4 is that I live through the timeline more than once. Scenario 5 pushes this idea even further: what if the spotlight did not move, but instead illuminated the entirety of the block universe. Instead of my sense of presentness moving through time, right now I permanently have only a sense of the present moment. For example, I am now sitting in front of my computer, and I will experience this present moment for eternity. But wait, you say, your phone is ringing and you are now getting up to answer it; isn't that now a new present moment for you? No, I reply, that is a future version of me who will for eternity experience the presentness of answering the phone. The I who writes this new sentence on my computer is yet another version of me locked into a conscious awareness of that task for eternity.
Just as scenarios 1-4 are consistent with my experience of presentness and time flow, so too is scenario 5. Here, now, is the punchline: scenario 5 is very much like static time theory, where all the events of my life are frozen within the block universe. Each frozen fragment of myself has only a fragment of consciousness. The illusion of time flow is simply memories that are passed on to me within my brain by my previous selves. The memory transfer is so seamless that I cannot tell which of these selves is me in my unique present moment, and none of my previous or future selves can do any better. This is certainly an unsettling explanation of the illusion of time flow, but, again, it is consistent with my private experience of presentness, and this is all that is required of static time theory. In short, in response to the critic of static time theory, even if my brain exists in fractured and frozen segments within the block universe, my brain still might be able to generate the illusion of time flow through accumulated memories.
Time Travel
One of the first fictional stories about time travel was Memoirs of the Twentieth Century, written in 1733 by Irishman Samuel Madden. In this work, the narrator says that he received letters from the future from a guardian angel, written by political diplomats who describe the social conditions of the nineteenth and twentieth-centuries. In Madden's book, no human actually travels to the future, and other than reliance on the guardian angel, he gives no explanation for how the letters have traveled back in time. Since Madden's day, time travel fiction has become sophisticated and abundant, and we are now so familiar with the concept that it would not surprise us if we learned that scientists discovered how to do it. But is time travel even possible?
The block universe theory suggests that we can indeed travel through time: if all events in the universe already exist, it seems that we should be able to move around in time just as we do in space. In an obvious sense, we are all traveling to the future right now at the rate of one second per second. Want to reach the future a little faster? Stand on a chair, and by being further from earth's gravity, which warps space-time, you'll shave off a trillionth of a second every day or so. Want to get there even faster? Go for a bike ride, and, according to the theory of special relativity, your increased speed will have a similar effect. While these involve microscopically small amounts of time reduction, it does show that accelerated time travel into the future is possible. Technology, like spacecrafts traveling near the speed of light, will dramatically magnify that change. For example, a five-year journey at 99.5% of light speed will move you 50 years into earth's future. Traveling to the past, though, is not as easy as flying fast in your spaceship, since, physicists tell us, your spaceship would need to exceed light speed, which is impossible. Still, physicists have offered theoretical suggestions for how time travel to the past might be possible, such as through worm holes that take short cuts from one part of spacetime to another.
While science suggest that time travel is "physically" possible, philosophers have discussed whether it is "logically" possible, and one way to test this is by examining time travel paradoxes, that is, time travel scenarios in which contradictions seem to arise. If the contradiction is genuine, then the time travel scenario that generated it is an impossible event and thus time travel cannot take place. Thus, defenders of time travel need to show that so-called time paradoxes have a work-around solution, and do not involve genuine contradictions. Let's look at four such paradoxes, which often appear in science fiction.
Second is the predestination paradox: Joe goes back in time to stop a mysterious serial killer; in his efforts he accidentally kills the wrong people, and thus becomes the serial killer that he was trying to stop. The contradiction is that Joe seeks to both stop and not stop the serial killer. The solution to this is also easy: there is no logical contradiction here but only an irony. Joe dislikes the effects of the alleged serial killer, yet he unknowingly is that killer.
Third is the bootstrap paradox, also called the causal loop paradox. Jane travels back in time to give past-Jane the instructions to build a time machine; she builds it, then travels back in time to give past-Jane the instructions to build a time machine. The contradiction is that the authored instructions appear without anyone authoring them. The solution is that this is not a genuine contradiction. It is certainly cheating to have the instructions simply appear without someone putting in years of hard work to research and write them. But cheating does not involve an explicit contradiction like "the instructions are authored and unauthored at the same time". Instead, the situation created by this paradox is that the instructions have always been unauthored. It is what philosophers call a "brute fact", that is, an event that has no explanation, such as the existence of the big bang or the existence of God. Brute facts are awkward, but not contradictory.
Fourth is the grandfather paradox: Jane goes back in time and kills her grandfather, which thereby prevents Jane from ever being born. The contradiction is that she does and does not exist during the same timeframe. This is the most commonly discussed paradox and there are several possible solutions. One solution is to recognize that the murder attempt obviously failed since Jane in fact exists and attempts to carry out the deed. No matter how many times she attempted the murder, they all ultimately failed. Another solution is that the murder did occur, but on a different timeline. Perhaps when Jane murders her grandfather, a new timeline branches off from this where Jane would never be born. However, the original timeline in which Jane was born continued uninterrupted.
There is some victory with the solutions to these paradoxes since they show that time travel is a theoretical possibility, that is, the concept of it is not a contradictory one. Whether our technology will ever produce a time machine is another question, but science nevertheless has the green light from metaphysicians to try.
The Ship of Theseus: Identity over Time
Another metaphysical puzzle about time is how physical objects retain their identity through changes over time. The ancient Greek historian Plutarch records a story about a legendary hero named Theseus who founded the city of Athens. After killing a monster, Theseus returned to Athens in his ship, and, to honor their leader, the city preserved his Ship for 1,000 years, replacing old boards one at a time as they rotted. Plutarch notes that "the vessel became an established illustration for philosophers regarding the proposed question of change, some declaring that it remained the same, others that it was not the same vessel" (Lives, "Theseus"). The question posed by the ship is a challenging one: how does the changing of a thing's parts affect the identity of the whole? This is not merely a theoretical issue, but, rather, it regularly arises with antique and vintage objects that had critical parts replaced. For example, someone might try to sell an old electric guitar that had its original electronics and hardware replaced, with nothing original remaining but the wood. The buyer then must make a judgement about the altered object's authenticity and value.
In more modern times, Thomas Hobbes extended this thought experiment further: what if the ancient Athenians had saved the old replaced boards and, at a later time, reassembled them into their original form. They would then have two complete ships: the first made from the new boards that progressively replaced the old ones (call this the "first ship"), and the second made from the old reassembled boards (call this the "second ship"). There clearly can't be two original ships, so which of the two is it, and what is the rationale for making that choice? Again, this is not merely a theoretical issue, and a case in point is the rock group "The Little River Band". The group started out with six members, who, one by one dropped out until not an original member was left. However, the original members later reunited, but legally could no longer call themselves "The Little River Band," since that name was owned by the reconfigured band with all new members.
There are two main solutions to the problem of the ship of Theseus. First is Hobbes's own solution: the second ship built from the reassembled boards carries the identity of Theseus's original ship. His argument rests on a classic philosophical distinction between matter and form: the first ship with the replaced boards retained the "form" of the original over time, while the second ship with the reassembled old boards retained the "matter" of the original. For Hobbes, when the issue has to do with the physical properties of objects, such as with ships and vintage guitars, the material stuff is more important than the original form. Thus, for Hobbes, it is the second ship made from the old reassembled boards that counts as the original.
However, Hobbes continues, the situation reverses when the issue has to do with things that inherently move or change, such as with a river that is always in flux, and in these cases the original form is more important than the material stuff. So, even though the physical water of a river comes and goes, the boundaries of its path carry the identity of the river. So too for the continued identity of a city: while its citizens come and go, the city's activities "proceed continually from the same institution, whether the [specific] men are the same or not" (De Corpore, 11). It is thus the form of the city which holds its identity through its never-ending changes, not its specific people. Using Hobbes's rationale, the legal decision regarding the identity of the Little River Band was the correct one: as with cities, the members of all music bands are in flux, so the name and identity goes with the reconfigured band with the new members. In short, for Hobbes, the second ship that is reassembled from the old boards is the original one, since the "matter" is what counts with physical objects like ships. By contrast, the original Little River Band is the one with progressively new members, since the "form" is what matters with things that by their nature change such as cities and musical groups.
The problem with Hobbes's solution is that it is incomplete: the notions of matter and form by themselves are inadequate to explain the ship's continued identity. The identity of the original ship cannot consist merely in the collection of original boards, because we could use those same boards to build a house, which obviously would not be the original ship. The identity of the original ship also cannot consist merely in the ship's shape or configuration, since we could build 1,000 similar ships using the same blueprint, and these obviously could not all be the original ship. The issue of the ship's identity is a more complex interplay between its matter and form as it moves through time.
A second and more modern solution, called four-dimensionalism, addresses the problem by locating the original ship's continued identity over time within the block universe. Again, Einstein describes the entirety of the universe as an unchanging four-dimensional block of space-time, where every event in the universe's history is already fixed somewhere within the block. For example, within the block universe, we could easily draw a dotted line around the three-dimensional ship of Theseus when the Atheneans first built it a few thousand years ago. Similarly, within the block universe, we can easily draw a dotted line around the ship from one point in time to the next even as its boards are replaced. The ship will have the form of something like a segmented worm, where each segment of the worm constitutes its three-dimensional shape at a different time slice within the block. Imagine, for example, an earth worm burrowed within a loaf of bread. The loaf is the block universe, and each segment of the worm is the ship's three-dimensional existence at a specific moment in time.
So, according to four-dimensionalism, which of the two ships is the original: the first with the newly replaced boards, or the second reassembled one from the old boards? Four-dimensionalism could go either way. As we trace the ship's history within the block universe, it will be like a segmented worm that splits into the shape of a Y. One split of the worm will be the refurbished ship, and the other split will be the reassembled ship. What we choose to count as the "original" ship, will be a matter of our preference based on what use we plan to make of it. If we plan to ceremonially take the ship out on the water year after year as the Atheneans did, then the refurbished first ship is the "original" for that purpose. Its ceremonial history is an important part of its continued identity. But if we plan to use the ship as a museum piece and do carbon 14 dating on it, then the reassembled second ship is the "original" for that purpose. Its physical state during the first time segment of its existence is an important part of its archival identity. Thus, the confusion of the ship's identity rests in its planned use, not in its status as a split worm that exists securely within the block universe. The block universe does not care which branch of the split constitutes the "original" ship, but we humans do care. The dilemma, then, is not a metaphysical one, but a sociological one.
C. ABSTRACT OBJECTS
Imagine that you fall into a black hole, and when you come out the other side you are in a strange reality that is outside of space and time. You no longer have a physical body, but with a special kind of mental vision you can perceive the presence of things around you. There are things like the shape of squareness, the number 5, the color greenness, the temperature of coldness, the animal species horseness. These things do not exist in any physical manner, but are more like the formula or blueprint of those notions. There are an infinite number of these things, and as you perceive each one you think, "OK, now I understand what I've been talking about all these years when using the words 'square', '5, 'green' and so on." Here we have one more science fiction-like world that philosophers since Plato have argued for, namely, the reality of abstract objects. In this section we consider arguments for and against the existence of these entities.
Realism
What exactly are abstract objects? The answer begins with a distinction between abstract objects and concrete objects. Concrete objects, such as the physical chair you are sitting on, (1) exist in space or time, (2) can go through changes, and (3) can causally move things. Your chair, for example, exists in identifiable parts of space and moments within time. It can change, such as when it breaks, and it can cause change, such as when the legs of the chair scratch the floor. There are different types of concrete objects, and here are the ones that philosophers commonly discuss:
• Physical things: a chair, a rock, a person
• Events: earthquakes, a birthday party
• Times: seconds, moments, years
• Places: my back yard, outer space
We all take it for granted that concrete objects exist since they comprise the obvious furniture of the world in which we all live, even if there is much about them that we still do not know. By contrast, abstract objects (1) do not exist in space or time, (2) do not go through changes, and (3) do not cause things to occur. Commonly discussed types of abstract objects are these:
• Universal properties: greenness, squareness, horseness
• Universal relations: smoothness, coldness, betweenness
• Mathematical entities: the number 5, pi, the null set
• Propositions: meaningful statements such as "the door is brown"
Take, for example, the abstract universal property of "squareness". There are obviously concrete objects that are square in shape, such as a Rubik's Cube: it exists in space and time, it gets scratches on it, and it produces a squeaky noise when I twist it. The abstract object squareness, though, is different: it does not exist in space and time, get scratches or squeaks. If we could destroy all square concrete objects in the physical world, the abstract object of squareness would still be there. An immediate question arises about abstract objects: if we can't perceive them, do they even exist? The theory of realism states that abstract objects do indeed exist, and the opposing theory of anti-realism states that they don't. Let's consider arguments for each theory.
The main defense of realism is the argument from indispensability: we need abstract objects to explain important things about the world that cannot be accounted for otherwise. Plato, for example, argued that there is a linguistic necessity for postulating abstract objects: there are many different physical horses that exist, each of which have their own unique differences. Yet they obviously share some common feature, otherwise we could not call them by the same name. That feature must be an abstract and enduring one that rises above all the variations in particular horses, which, according to Plato, is the abstract Form of "horse" that exists in a higher spirit- realm of Forms. Thus, for Plato, we need the abstract object of "horse" to explain our use of the word "horse" with concrete things like the horse in my neighbor's barn.
A more compelling example of the indispensability of abstract objects is with mathematical entities, which we need for our best scientific theories about the world. Scientists often postulate the existence of what are called "theoretical entities", that is, unobservable objects that we presume to exist because doing so helps explain an important scientific phenomenon. For example, while dark matter has never been directly observed, presuming its existence helps explain how galaxies rotate and why the universe is expanding at the rate that it does. Similarly, with abstract objects, numbers themselves are theoretical entities that scientists must assume since all science depends upon them. Furthermore, mathematics abounds with existence claims, such as "there exists a prime number between 3 and 7" or "There exists a number such that three times that number minus 5 is equal to 40." Put simply, reference to the number 5 implies that 5 exists. These numbers cannot be concrete objects that exist somewhere in space and time, like a chair or a speck of dust in outer space. Rather, they are thus best understood as abstract objects. Stated more formally, the argument from indispensability is this:
(2) Abstract mathematical entities are indispensable to our best scientific view of the world.
(3) Therefore, we may assume that abstract mathematical entities exist.
Premise 1 is called the "indispensability thesis", and it aims to restrict conjectures about metaphysical entities to situations of dire scientific need. Premise 2 states that mathematical entities fit that situation of dire need. Premise 2, then, is the assumption that anti-realism rejects, which we turn to next.
Anti-Realism: Nominalism and Conceptualism
The main argument for anti-realism is the "principle of simplicity" or "Ockham's Razor" as it is often called: when possible, we should adopt simpler explanations over complex ones. As Aristotle words it, "all other things being equal, we may assume the superiority of demonstration that derives from fewer postulates or hypotheses" (Posterior Analytics, 25). Aristotle himself uses this principle when arguing against Plato's realist theory of the Forms: what, he asks, "do the Forms contribute to sensible things here on earth. . . . for they cause neither movement nor any change in them" (Metaphysics, 1.9). For Aristotle, we can adequately explain existing things without appealing to entities in a higher abstract realm. Similarly, medieval philosopher William of Ockham famously uses the principle of simplicity to reject realist theories of universals, essentially cutting away such entities with a razor. His own wording of the principle is that "Plurality is not to be posited without necessity" (Sentences, 1.1). For Ockham, by proposing any metaphysical entity, we are thereby adding one more thing beyond the facts in the tangible world that we already accept. In Plato's case, we already accept the physical world of appearances, but now, in addition to this, Plato asks us to accept the existence of a spirit-like realm of eternal truths.
So, if concepts like "greenness" and "5" are not abstract objects, what according to anti-realists are they? There are two common answers, one called "nominalism" and the other "conceptualism". Nominalism, which literally means "name-ism", is the view that there are no abstract objects and we simply apply general words to similar experiences. I see several colors that appear similarly, and I apply the name "green" to them. I repeatedly see a specific quantity of things and I apply the name "5" to that quantity. While it might seem as though statements with the words "green" and "5" are about abstract universal objects, they are not. According to a version of this theory called "paraphrase nominalism", these terms can be rephrased as statements about concrete particular objects. Take, for example, the sentence "the tree in my front yard is green", which on face value implies the existence of an abstract entity of greenness. However, I can rephrase this as follows:
This makes no assertion about the metaphysical existence of an abstract universal object of greenness, but instead restricts "green" to how we use the word in English. Similarly, with mathematical entities, take the following statement "2+3=5"., This equation can be rephrased as an if-then sentence, which avoids any realist assumption that "2" "3" and "5" are abstract entities:
If there were such things as numbers, then 2+3=5.
Worded in this way, there is no commitment to the existence of abstract mathematical objects. An even easier rephrasing is this:
2+3=5, but no mathematical entities exist.
In this case, we have the original mathematical equation, but a denial of abstract mathematical entities.
Another approach to anti-realism is called "conceptualism", which is the view that there are no abstract objects, and abstractions such as "greenness" and "5" are merely mental concepts. Ockham himself was a conceptualist and argued that when we speak about "greenness" or the number "5", our words refer to the intentions of particular minds. Take again the sentence "the tree in my front yard is green". For the conceptualist, this means the following:
Mental concepts that apply to the color green also apply to the tree in my front yard.
A problem for the conceptualist to solve is, why do different people have the same mental concepts of "horseness" and "5", rather than completely different ones. That is, what is it about the human thought process that enables each person to form the same abstract ideas? Ockham, for example, would need to show that what I intend by the word "horse" is the same as what you intend by it. While Ockham himself provides no such explanation, during the modern period of philosophy, most of the major thinkers were conceptualists, and each offered a detailed psychological theory of abstraction. Descartes, for example, boldly states that "number and all universals are simply modes of thought" (Principles, 1.58), which for him involves physical patterns that are directly imprinted on the brain itself. Each time I see a horse, a "horseness" pattern becomes more firmly embedded on my brain, and eventually this makes a permanent mark, perhaps as a tiny hole or brain fold. When I then see another horse, my mind scans through all the imprints on my brain until it finds the "horseness" pattern. Descartes of course got his brain science wrong. Nevertheless, his conceptualist theory removed the question of abstract objects from metaphysics and placed it in the realm of physics. This continues in our own time as cognitive neuroscientists and computer scientists alike study the process of pattern recognition.
Between realism and anti-realism, then, which is the better theory of abstract objects? The answer ultimately rests on one's view of metaphysics as a whole. If you are already persuaded that a non-physical world exists that contains entities like Gods and spirits, as Plato did, then it's easy to extend that realm to include intangible abstract objects as a means of resolving scientific puzzles. On the other hand, if you think that scientific explanations should be restricted to the tangible realm, then you will seek for linguistic or psychological explanations of abstract objects. So far we have looked at two types of abstract objects that metaphysicians discuss: universal properties like greenness, squareness, horseness, and mathematical entities like the number 5. In the next section we will explore whether fictional characters in literature have any special abstract metaphysical existence.
Fictional Objects
Legends, books, and movies abound with fictional characters that entertain us and bring out our emotions towards them. As a sample, consider these statements:
• The Easter Bunny hides decorated eggs.
• Huck Finn lived in Missouri.
• Spiderman was bitten by a spider as a boy.
While it is clear that these characters do not exist in the way that you and I do, we believe that the above statements are true. Based on the above facts, we might deduce further truths like "the Easter Bunny has artistic ability," "Huck Finn lived west of the Mississippi River," and "Spiderman once came in contact with an arachnid." Even if I say "I don't believe in the Easter Bunny", I need to assert him before I can deny my belief in him. Our ordinary talk about fictional truth raises the question about the type of existence that fictional characters have.
David Lewis attempted to explain our talk about fictional characters by linking them with concrete possible worlds: the Easter Bunny is a concrete object, but only in an alternative universe, not in this one. At the outset of this chapter we looked at Lewis's view that possible worlds are like alternate realities that have concrete existence, some like our own world and others not. According to Lewis, if I say that "the Easter Bunny hides decorated eggs," I mean that "in some possible world there is an Easter Bunny who hides decorated eggs." In our actual world, then, statements about the Easter Bunny are fictionally true because they point to a concrete possible world in which the Easter Bunny genuinely exists. So too with fictionally true statements about Huck Finn and Spiderman. Lewis's view, though, is pretty extreme, and few of us would claim to believe that in some possible world there is a genuine Easter Bunny that hides decorated eggs for children on Easter Sunday.
A more moderate approach would be to link fictional characters like the Easter Bunny with abstract objects, rather than concrete ones. But, this suggestion immediately faces a problem: as we've seen, abstract objects exist outside of space and time, and the Easter Bunny tradition was created at a very specific point in space and time by eighteenth-century German immigrants to the U.S. Consequently, the Easter Bunny cannot be an abstract object since it lacks the essential feature of timelessness. This is not a problem for the number 5, for example, since numbers are not cultural creations, and so it presumably can exist outside of space and time. But, it does not make sense to say that any fictional character that I invent could instantly have the same metaphysical status as numbers.
An alternative metaphysical solution is to say that the Easter Bunny is an "abstract artifact", that is, an abstract entity created by humans. Abstract artifacts are not the same thing as abstract objects. An "artifact" is something that is created at a specific point in time, whereas an abstract "object", as we have seen, is outside of space and time and as such is uncreated. The notion of an abstract artifact is a recent theory, and its defenders suggest that there is always room for another class of things within the larger world of abstract entities. A benefit of the theory of abstract artifacts is that it conveniently fits into our legal conception of intellectual property, which includes literature, music, art, and software. While these can be represented in concrete form, such as a physical book or a musical performance, the item of intellectual property is a more abstract thing, or an idea, that has the capacity of being put into tangible form. Thus, according to abstract artifact theory, we should view all fictional characters such as the Easter Bunny as abstract artifacts that were created at a particular moment in time and have a non-concrete existence.
What would an anti-realists say about this account of fictional objects? While it is theoretically possible that the Easter Bunny could be an abstract artifact, it is still an extreme assumption to make merely for the sake of our amusement with fictional characters. It may be scientifically indispensable to postulate the existence of black holes or even abstract mathematical entities. But there is no such urgency to postulate the abstract existence of fictional characters like the Easter Bunny. It fails the indispensability thesis, which we described earlier. A nominalist would say that fictional characters are just figures of speech and nothing more. We can easily rephrase statements about the Easter Bunny without making any assumptions about its real existence, such as the following:
If there were such a thing as the Easter Bunny, it would hide decorated eggs.
With this rephrasing, nothing implies that the Easter Bunny exists, or that we are making factually true statements about it. What we do say about the Easter Bunny is all hypothetical.
Similarly, conceptualists would go a step further and say that fictional characters are just mental concepts, and we can give a psychological account of how humans come up with them. Again, most of the major modern philosophers had conceptualist theories of how the human imagination constructs fictitious ideas. Descartes argues that the imagination is an activity of the brain that produces dreams, fantasies, musings and hallucinations. The idea of a winged horse, for example, comes about by assembling memories of a horse and birds wings that are stored in the brain. For Descartes, then, fictional objects like the Easter Bunny would simply be a mental assemblage of memories about bunnies, eggs, charity and Easter. Today, a more detailed account of how we conceptualize fictional characters is best answered by cognitive psychology, not through metaphysical speculation.
Substance: Substratum Theory vs. Bundle Theory
Imagine that you have no knowledge whatsoever about modern science, and your technology is limited to wooden huts and clay pots. You are curious about how the world works and you see an endless variety of natural things, such as rocks, dirt, trees, lakes, fire. You know that, combined in the right way, these things can transform into even more kinds of things. Wood mixed with fire produces smoke and ashes. Clay mixed with water and fire produces pottery. It occurs to you that, beneath this variety, there may be an underlying stuff which when manipulated the right way takes on different characteristics. There is, you conclude, a mysterious underlying substance of all these things which holds together the overlying qualities or attributes that these things take on. Without any knowledge of real science, then, you have developed a metaphysical description of the natural world around you involving the notions of substance and attribute. Ancient philosophers went through the same reasoning process and, after over 2,000 years these concepts are still central to metaphysics.
Philosophers have used the term "substance" in different ways, but we will focus on one originally proposed by Aristotle and later developed by John Locke. On this view, a substance is a support or substratum of attributes, where the substance of a thing is spread beneath the attributes. For example, the underlying substance of a tree is like a container that holds the attributes of greenness, brownness, hardness. The tree's substance is a concrete thing, but the tree's attributes are abstract universal properties. To avoid confusion, we will use the term "substance-substratum" to designate this conception of an underlying substance. Philosophers have disagreed about how many substance-substrata exist, and the answer depends on whether the philosopher is a monist, dualist or pluralist, as laid out here:
• Monistic idealism: there is only one substance-substratum in the universe, which is the spirit-mind of God.
• Dualism: There are two substance-substrata in the universe, one of which is matter and the other spirit-mind.
• Pluralism: There are many substance-substrata in the universe, one for each concrete particular object like a tree.
For our purposes, we will think of substance-substrata in the pluralistic sense, where each concrete particular object like the tree in my front yard has its own substance.
The question that we now address is whether there really is a substance-substratum that lies beneath the attributes of an object like a tree. There are two rival answers: substratum theory says yes, and bundle theory says no. According to substratum theory, the tree's substance-substratum is the glue that holds together its various attributes of greenness and brownness. The substratum glue helps address two problems, the first is how to distinguish between two objects with the same attributes (sometimes called the problem of individuation). Suppose I have two virtually indistinguishable trees, one in my front yard, the other in my back yard. While they may have the same attributes, such as their shape and color, they each have their own substance-substratum, which accounts for them being numerically different objects. The second problem that it solves is how an object retains its identity when its attributes change (sometimes called the problem of persistence). For example, the tree in my front yard can lose its green leaves, but it is still the same tree since its substance-substratum remains the same. Here, then, is the main argument for substratum theory: we are justified in postulating the existence of a tree's substance-substratum, since without it we could neither distinguish one virtually identical tree from another, nor trace a single tree's identity through changes over time.
Aside from being a kind of glue, what exactly is a substance-substratum? Locke himself says that this question cannot be answered:
if any one will examine himself concerning his notion of pure substance in general, he will find he has no other idea of it at all, but only a supposition of he knows not what support of such qualities, which are capable of producing simple ideas in us; which qualities are commonly called accidents. [Essay, 2.23.2]
Elsewhere he similarly states that a substance-substratum is merely a "something, I know not what" (Examination of Malebranche, 26). Everything that we know about a tree consists of attributes that we experience, such as the greenness of its leaves and brownness of its bark, and its substance-substratum is hidden beneath those attributes. For Locke, we know it is there since something must pull all the attributes of the tree together into a single concrete tree. It's there, but its nature is unknowable.
Substratum theory thus maintains that there are two metaphysical components to a particular tree: first is the underlying substance-substratum that is unknowable, second are the attributes such as greenness and brownness, which, according to substratum theorists, are abstract universal objects. That's a lot of metaphysical baggage that the poor tree needs to carry around. Does the tree really need it? No it doesn't, says the rival position of bundle theory. On this view, a particular tree has no substance-substratum, and the tree is only a bundle or cluster of attributes. There are two parts to bundle theory, the first of which aims to eliminate the underlying substance-substrata. According to bundle theorists, if substance-substrata are beyond the reach of experience, as Locke suggests, this alone makes it suspect. The only justification for supposing that it is even there is that it presumably serves as a glue for holding together the attributes of a tree. But there are other ways of accounting for this glue that do not involve postulating the existence of a hidden and unknowable substance-substratum.
The second part of bundle theory attempts to show how attributes in a bundle can be self-gluing, and philosophers have proposed various explanations. One theory suggests that the tree's attributes of greenness and brownness are self-clumping through a relationship of "togetherness" (sometimes called co-instantiation). Another theory suggests that attributes like greenness and brownness are not over-arching universal properties, but are instead particular properties that self-clump into a single tree (sometimes called trope theory). While both of these approaches deny the metaphysical existence of substance-substrata, they still hold onto the metaphysical status of the self-gluing attributes. The tree's metaphysical baggage is now a little lighter, but still weighty.
There is, though, a thoroughly anti-realist account of bundle theory that eliminates the remaining baggage of metaphysical properties. Following the theory of conceptualism discussed earlier, the tree's attributes of greenness and brownness are not bundles of metaphysical entities, but instead are bundles of concepts in our brains. Take for example the statement "the tree in my front yard is green and brown." For the conceptualist this means the following:
The set of mental concepts that apply to green and brown also apply to the tree in my front yard.
Again, any more detailed explanation bout how this conceptualization takes place within our brains is the task of cognitive psychology, not philosophy.
D. CRITICISMS OF METAPHYSICS
The history of philosophy is filled with creative metaphysical explanations of the world around us. They are convenient solutions to troubling problems, and they add structure to our fragmented experiences. But metaphysics risks being like bad science fiction: while great detail is paid to strange entities, they are not always believable. Thus, critics argue, while we may be drawn to metaphysical conjecture, perhaps we should resist that temptation. We have already looked at criticisms of various metaphysical realities, and several times the principle of simplicity as come up as a reason for rejecting them. Generally speaking, simplicity will prefer non-metaphysical explanations of things over metaphysical ones. We already believe in the physical world, and if we can restrict our explanations to that, then metaphysical explanations are an unnecessary add on. Simplicity thus attempts to rein in metaphysical efforts and replace them with more tangible alternatives. Philosophers typically appeal to simplicity when narrowly focusing on specific metaphysical claims, such as the existence of universal abstract objects. But simplicity is less convincing as an overarching critique of metaphysical reality, since, at our current stage of knowledge, we don't know enough about reality to rule out any plausible explanation. We see this in contemporary physics with their complex theories of multidimensional universes, which have a strong metaphysical feel. For all we know, multi-dimensionalism might be true, and we do not want to prematurely dismiss this type of metaphysical speculation solely on the basis of the principle of simplicity. There are, though, other criticisms of metaphysics that do attempt to bury the entire enterprise once and for all. In this section we will look at three such global anti-metaphysical critiques: Kantianism, logical positivism, and scientism.
Kant: The Human Mind cannot Access Metaphysical Reality
Our human minds are designed to do some things pretty well. We can sense objects in our immediate surroundings, such as cars on the road that we try to avoid while crossing it. In a crowd of thousands of strangers, I can seek out and recognize friends and family members. Other things our minds are not designed to do so well. If I drop a coin and it hits the floor, my mind cannot tell by its mere sound where the coin finally rested, and I have to crawl along the ground like an animal to find it. When a star explodes on the other side of the galaxy, I have no perception of it even if I am staring directly at that point in space. There are thus clear constraints to what our minds can understand about the physical world. German philosopher Immanuel Kant (1724-1804) argued that the matter is much worse when it comes to our mental ability to access the metaphysical realm: we cannot do it at all. Our minds naturally form conceptions that help us make sense of the world, such as when I devise the abstract idea of greenness which allows me to group together many green things. But the abstract entity of greenness does not actually exist and is instead a creation of my mind. All metaphysical notions for Kant are the same: they are mental constructs that may or may not have anything to do with the actual world. We've already seen the conceptualist critique of abstract objects, and Kant is just extending this to the entire range of metaphysical notions.
There are two parts to Kant's critique, the first of which is his distinction between the phenomenal and noumenal realms. We spoke earlier of a barrier that exists between our minds and the external world, where our minds create an image of reality that may be influenced by external things, but, at the same time, we have no direct access to that external reality and do not know what it is truly like. This, for Kant, is the barrier between the phenomenal and noumenal. That is, the phenomenal realm consists of things as they appear to our senses, which ultimately relies on our mental machinery. The noumenal realm, by contrast, consists of things that are unknowable through our senses and permanently blocked from our minds. These unknowable realities he calls "things in themselves": they are "transcendent" in that they are outside of all possible human knowledge, and independent of human observation. For Kant, these transcendent noumenal things include many alleged metaphysical entities discussed by philosophers, such as a unified self, God, free will, and immortal souls.
The second part of Kant's theory is his explanation of our mental machinery that enables us to construct the phenomenal world of appearances in a meaningful way. For Kant, our minds to this automatically. For example, when I step out of my house in the morning, I am flooded with perceptual information about my front yard, which consists of a chaotic mix of colors, sounds, smells, tastes and textures. The first thing my mind does is organize them within my present position in space, and my present moment in time. I see my sidewalk in three-dimensional space and rapidly changing in time as I walk down it. He calls these "intuitions" of space and time. Next, my understanding imposes conceptual patterns on what I experience that enable me to make judgments about it, and these patterns he calls "categories". I look at the newspaper on my sidewalk and, through the category of unity, I judge that there is a singular newspaper resting there. I glance at the green yards in my neighborhood and, through the category of totality, I judge that all grass is green. I see that my grass is overgrown, and, through the category of possibility, I judge that, with the help of my lawnmower, my lawn could look better. Kant lists twelve such categories that serve as filters for everything we perceive. They are so essential to how we understand the world that he calls them "the lawgiver of nature" (Critique of Pure Reason, 1.2.1). That is, nature is not found in the inaccessible noumenal realm, but rather within our mental categories that organize our sensory data. According to Kant, traditional metaphysics went wrong by randomly groping for things within the inaccessible noumenal realm. The only true "metaphysics", if we wish to call it that, is in fact psychology and its study of our mental categories, which will ultimately clarify the narrow limits of the human mind.
How might a defender of metaphysics respond to Kant? Even if our judgments about the world are restricted by our mental categories, this does not completely rule out inferences about metaphysical realities in the noumenal realm. Kant himself attempted to do this by arguing that we are entitled to postulate the existence of God, human free will and the immortal soul because these metaphysical realities are necessary for morality. That is, for morality to be meaningful, we need to make free choices, and we need to be held accountable for our choices in the afterlife by a divine judge. Some followers of Kant similarly held that the experience of artistic beauty allows us to peak over the barrier into the noumenal realm and have a glimpse of things in themselves.
This tactic, though, seems a little too convenient, and any philosopher could come along and insist on the urgency of accessing the metaphysical realm for a pet cause, whether it be religion, morality or art. Nevertheless, the takeaway message of Kant's theory is that there is no peaking over the barrier, and, while his understanding of human psychology is dated, this is the main point of his theory that lives on. A famous expression within post-modern philosophy is that "there is nothing outside the text," which means that we cannot view the world from outside of our conceptual framework. This is bad news for the traditional metaphysician.
Logical Positivism: Metaphysical Statements are Meaningless
Here are some ordinary statements that we all find meaningful:
• The Eifel Tower is in Paris
• George Washington was the first U.S. president
• 1+1=2
• All bachelors are unmarried men
Here, by contrast, are some statements that we would say are meaningless:
• The Eifel Tower has an undetectable flavor of bacon
• George Washington is the enigma of the universe
• 1+1 equals free admission to an alternate timeline
• All bachelors were married to bachelorettes by angels without anyone knowing about it
Consider now some metaphysical statements that philosophers make:
• God is identical to nature as a whole
• Humans have the ability to have done otherwise
• Absolute Mind is the content and shape of its truth
• Abstract universal objects exist in a mind-independent reality
Are these metaphysical questions more like the first set of meaningful statements, or like the second set of meaningless ones? According to a philosophical school called "logical positivism", metaphysical statements are like the meaningless ones. It's not that they are false, but rather they are meaningless because they have no factual content that we can even judge to be true or false. Take, for example, the above two statements about the Eifel Tower. When I say that "the Eifel Tower is in Paris," this is a claim that I can verify, such as by traveling to Paris and standing in front of it. But there is no mechanism by which I can verify the truth or falsehood of the statement "The Eifel Tower has an undetectable flavor of bacon". I can put my tongue against it as much as I like, and submit it to a battery of scientific experiments, but all this testing will prove nothing since the alleged bacon flavor is undetectable. So too with metaphysical statements such as "abstract universal objects exist in a mind-independent reality". No conceivable test can demonstrate either the truth or falsehood of this statement.
The school of logical positivism emerged in the early twentieth-century in reaction to incomprehensible metaphysical theories such as Hegel's, and their stated goal was the elimination of all metaphysics. Philosophers like Hegel, they argued, have fallen into a trap of thinking that their metaphysical claims are actually about something, when in fact they are just linguistic nonsense. One of the main proponents of this position was British philosopher Alfred Jules Ayer (1910-1989). The logical positivist's critique of metaphysics, he argues, is not the same as Kant's. For, according to Kant, it is the limitations of our psychological makeup that prevents us from conceptualizing metaphysical realities which, for all we know, might actually exist. According to Ayer, though, the logical positivist critique is linguistic: the metaphysical statements themselves are meaningless since they lack factual content that we can verify. Central to logical positivism's position is its principle of verification, which is a litmus test that every proposition must pass to count as meaningful. Ayer presents this principle here:
The principle of verification is supposed to furnish a criterion by which it can be determined whether or not a sentence is literally meaningful. A simple way to formulate it would be to say that a sentence had literal meaning if and only if the proposition it expressed was either analytic or empirically verifiable. [Language, Truth and Logic, Introduction]
The test Ayer offers is two-pronged: meaningful statements are either (a) analytically true, that is, true by definition, or (b) empirically verifiable, that is, some possible experience will either confirm or disconfirm it. With this latter prong, Ayer says that, for a statement to be empirically verifiable, I am not required to actually perform the task of verifying it. Rather, I only need to have a verification procedure that is at least plausible. For example, the statement "flowers are growing on mars" is meaningful since we could theoretically construct a super telescope that could scan the entire planet and either confirm or disconfirm this statement. But I don't actually need to build the telescope for the statement to be verifiable.
Look again at the above list of meaningful statements. As we've seen, "The Eifel Tower is in Paris" is meaningful since we can travel there and empirically verify it. We can also empirically verify historical statements such as "George Washington was the first U.S. president" by looking at the historical evidence, which overwhelmingly supports this claim. The statements "1+1=2" and "all bachelors are unmarried men" are meaningful, not because they are empirically verifiable, but because they are true by definition. But when we move on to the above list of metaphysical statements, they all fail both prongs of Ayer's test: they are neither true by definition, nor are they empirically verifiable. For example, if I say that "God is identical to nature as a whole", I am not claiming that the word "God" by definition includes the notion of being identical to nature as a whole. Also, my statement that "God is identical to nature as a whole" cannot be empirically verified since I cannot conduct an interview with God and ask him about this. Even if I could fly to the edge of the universe and look down on it in its entirety, this could not reveal whether what I was looking at was God. We face similar problems with each of the other metaphysical statements: there is no possible experience that will either confirm or disconfirm it. Metaphysical utterances like these, according to Ayer, do not even count as propositions, but are only pseudo-propositions: they at first appear to be verifiable, but turn out to be not so. He writes that "The sentence expressing it may be emotionally significant to him [who utters it]; but it is not literally significant."
For a few decades, logical positivism struck fear in the hearts of philosophers who risked being accused of uttering nonsense if they made metaphysical claims. But logical positivism came under attack because of a built-in problem it has: logical-positivism's verification principle is self-refuting. Here is their principle:
a statement is meaningful if and only if it is either true by definition or empirically verifiable
We now must ask: is this principle itself true by definition? No, it is not. Is this principle itself empirically verifiable? No, it is not. Thus, according to the critic, the verification principle fails its own test and is therefore meaningless; it is a mere pseudo-proposition. Logical positivists responded that they intended their verification principle to be just a recommendation, and not a demand or factual claim about the world. But this response does little to help their cause, since why would a metaphysician ever accept such a recommendation that would have the effect of putting metaphysicians themselves out of business? While the verification principle thus fails as a decisive refutation of all metaphysics, it still haunts philosophy. Though metaphysicians are not necessarily required to abide by the verification principle, there is still a lingering suspicion that they are uttering nonsense when making metaphysical claims. Once again, this is bad news for the traditional metaphysician.
Scientism: Reality is the Domain of Science, not Metaphysics
A third sweeping critique of metaphysics, associated with a view called "scientism", is that scientific methodology is a better approach to understanding the world than is the methodology of metaphysics. The term "scientism" is typically used in a derogatory way by critics who believe that some advocates of the scientific method have gone too far by claiming that science is the only way of describing the world, thereby rejecting metaphysical, theological or humanistic methods of inquiry. For our purposes, we will not be using "scientism" in this extreme way, but rather in a more moderate sense defined as follows: science offers the most reliable and promising method of describing the world and should thereby be preferred over non-scientific methods. The claim here is not that science is the "only" acceptable method of inquiry, but, instead, that it should be the default method of inquiry since modern science's track record has been so successful. Non-scientific methods may be preferable in areas that have been inadequately explored by science, such as matters of beauty and love. But metaphysical claims do not deserve that privileged position.
When metaphysics emerged in ancient Greece 2,500 years ago, there was no rigorous scientific method and thus metaphysics was the best science of the day. Ancient metaphysicians speculated about subjects like the primary element from which everything is made, the smallest particles of matter, and the swirling vortex of the cosmos. It was clearly an attempt to explain hidden features of the world in a scientific-like way. Metaphysics afterwards expanded into all the issues covered in this chapter, such as abstract objects, always claiming to be making scientific-like discoveries about the world. But genuine science and the scientific method dramatically developed since those early days, and the scientific approach has since proven to be the most fruitful and reliable source of knowledge about reality. When metaphysics claims to describe the world, it is following a dead-end methodology that is neither truly scientific, nor a supplement to science, nor a replacement of genuine science. It is a clumsy relic of the past that serves only to entertain philosophers and mislead everyone else. The argument against metaphysics from scientism is not the same as that of logical positivism: it is not a critique of the linguistic intelligibility of metaphysical claims, but rather a critique of how traditional metaphysics disregards genuine science.
This critique of metaphysics from scientism is explored in the book Everything Must Go (2007), coauthored by James Ladyman and Don Ross. The authors argue that modern science has provided adequate grounds for rejecting many of the claims made by metaphysicians. Metaphysics, they argue, rests on unfounded appeals to intuition at the expense of doing real science to answer questions about the world, and such speculations have "no more in common with reality as physics describes it than does the ancient cosmology of four elements and perfect celestial spheres". Traditional metaphysics thus "contributes nothing to human knowledge and, where it has any impact at all, systematically misrepresents the relative significance of what we do know on the basis of science." The key problem, they argue, is that metaphysical arguments rest on intuitions that seem plausible yet have nothing to do with the truth. They are more like artistic speculations and "have more in common with the virtues of story-writing than with science." During human evolution, our intuitions about the world formed as a way to track medium-scale objects like antelope that we can chase and eat, and lions that we need to run away from. These intuitions have little to do with small-scale objects like sub-atomic particles, or large-scale objects like galaxies and black holes. Accordingly, "there is no reason to imagine that our habitual intuitions and inferential responses are well designed for science or for metaphysics." Mathematical reasoning is what enables us to grasp the tiny reality of atoms and the enormous galactic universe, not our intuitions. As scientifically-minded naturalists, the authors argue, "we are not concerned with preserving intuitions at all."
While the authors conclude that traditional metaphysics should be rejected, they believe there is still a role for what they call "naturalistic metaphysics": metaphysics should only attempt to offer a unified and cross-disciplinary explanation of what specific sciences tell us about reality. This neither goes against science nor operates independently of science. Rather, it is like a mediator between different branches of science that attempts to bring together work on related issues, which "jointly explain more than the sum of what is explained by the two hypotheses taken separately".
What should we think about this critique of metaphysics from scientism? Much of it is undeniable. Metaphysics often puts forward theories about the world that have nothing to do with science, and are even in conflict with it. This was the case with Bergson's metaphysical defense of time flow, which conflicted with Einstein's scientifically-based view of the block universe. However, in defense of metaphysics, metaphysical philosophy has always played an important role as a breeding ground for new ideas about the world that often later developed into independent branches of science. In past centuries, every science was part of philosophy, where the hard sciences of physics, chemistry and biology were grouped under "natural philosophy," and the social sciences of psychology, economics and sociology were grouped under "moral philosophy". One by one these sciences moved on from their philosophical birthplace, which ultimately left a non-scientific core of philosophy dominated by metaphysics. This reveals the instrumental role that traditional metaphysics played in the early stages of these disciplines, before they gained a secure foothold of scientific methodology. If there still are any components of philosophy that have scientific viability, it is just a question of time before they too will be taken possession of by one of the established sciences, or splinter off into their own new scientific field.
Still, the critique from scientism is bad news for the metaphysician, as was also the case with the critiques by Kant and logical positivism. It is not because these three arguments against metaphysics are conclusive. They are not, they all have weaknesses. The bad news is that, in spite of their weaknesses, these three critiques, in one form or another, are lingering. However much the metaphysician attempts to justify postulating a metaphysical entity, the immediate reaction is that such notions are only fabrications of the mind, or that they are unverifiable, or that they do not match what science tells us about the world. This means that, from the start, the metaphysician is on the defensive.
REFERENCES
Aristotle, Metaphysics, 1.9.
Ayer, Alfred Jules, Language, Truth and Logic (1936), Introduction.
Berkeley, George, A Treatise Concerning the Principles of Human Knowledge (1710), 3.
Bostrom, Nick, "Are You Living in a Computer Simulation?" Philosophical Quarterly (2003) Vol. 53.
Cavendish, Margaret, Blazing Worlds (1666).
Descartes, Rene, Principles of Philosophy (1644), 1.58.
Hegel, Georg Wilhelm Friedrich, Phenomenology (1807), Preface.
Hegel, Georg Wilhelm Friedrich, Philosophy of Right (1810), Preface.
Hobbes, Thomas, De Corpore (1655), 11.
James, William, The Principles of Psychology (1890), 6.4
Kant, Immanuel, Critique of Pure Reason (1781), 1.2.1
Ladyman, James and Ross, Don, Everything Must Go (Oxford: 2007).
Leibniz, Gottfried Wilhelm, New Essays (1704).
Lewis, David, On the Plurality of Worlds (Oxford: Blackwell, 1986).
Locke, John, An Essay Concerning Human Understanding (1690), 2.23.2.
Locke, John, Examination of Malebranche (1706), 26.
Madden, Samuel, Memoirs of the Twentieth Century (1733).
Plato, Republic 10, 596.
Plutarch, Lives, "Theseus".
Russell, Bertrand, The Philosophy of Logical Atomism (1918), 3.
Schopenhauer, Arthur, The World as Will (1819), 2.1.25.
Stapledon, Olaf, The Star Maker (1937).
William of Ockham Sentences, 1.1.
STUDY QUESTIONS
Please answer all 21 of the following questions.
1. Define metaphysics, monism, materialism, idealism, and dualism.
2. What is Berkeley's subjective idealism, and what is his argument for it?
3. What is Hegel's absolute idealism, and what is his argument for it?
4. What is panpsychism, and what is the argument for it?
5. What is the combination problem of panpsychism, and a solution to it?
6. What are the various possible structures of time?
7. Describe the dynamic and static theories of time.
8. What are the four paradoxes of time, and what is the purpose of discussing them?
9. What is Hobbes's solution to the ship of Theseus problem?
10. What is the block universe solution to the ship of Theseus problem?
11. What are the three features of concrete objects and abstract objects respectively?
12. What is the argument for realism from indispensability?
13. What is Lewis's theory and the abstract artifact theory of fictional objects.
14. Describe the anti-realist views of nominalism and conceptualism.
15. What is the main argument for substratum theory?
16. Describe bundle theory.
17. Describe Kant's notions of the phenomenal and noumenal realms and his critique of metaphysics.
18. Describe logical positivism's verification principle, and its critique of metaphysics.
19. What is the criticism of logical positivism's verification principle?
20. Describe Ladyman and Doss's argument against metaphysics from scientism, and their view of naturalistic metaphysics.
[Short Essay]
21. Short essay: pick any one of the following views in this chapter and criticize it in a minimum of 100 words. Berkeley's subjective idealism; Hegel's absolute idealism; panpsychism; the dynamic theory of time, the static theory of time, one of the time travel paradoxes; Hobbes's solution to the ship of Theseus problem; the block universe solution to the ship of Theseus problem; the argument for realism from indispensability; the anti-realist views of nominalism or conceptualism; substratum theory; bundle theory; one of the theories of fictional objects; the critique of metaphysics by Kant, logical positivism, or scientism.