This page: full notes A* summary notes C/B summary notes
Dualism: the view that there are two different types of existence: mental and physical.
Substance dualism: Descartes’ version of dualism that the two different types of existence are two different substances, e.g. mental (characterised by thinking) and physical (characterised by extension). A substance is a type of existence which cannot be broken down into anything further.
Monism: the view that there is one kind of existence.
Materialism: the view that the one kind of existence is physical substance.
Plato believed the body was like a prison for the soul, trapping it in this world of appearances. He thought our souls came from the world of forms and had a vague memory of the forms.
Look up charioteer analogy
Plato’s argument from recollection
The argument from recollection is one of Plato’s arguments for the existence of the world of forms and also the existence of the soul.
Plato points out that we somehow do have knowledge of perfect, eternal and unchanging concepts. These include concepts like perfect beauty and justice. We also have perfect mathematical concepts and geometric concepts such as the idea of a perfect circle or two sticks being perfectly ‘equal’ in length. We have never experienced perfect beauty, justice or a perfect circle. So, we must have gained this knowledge a priori. In The Meno Plato tells the story of how Socrates proved that an uneducated slave boy could be prompted by a series of questions and some shapes drawn in the sand to figure out how to solve a geometry question. The slave boy must therefore have been born with geometric concepts.
Plato then seeks to explain how we could have been born with these concepts. His answer is that we must have somehow gained these concepts before we were born. It follows that there must be a part of us (our soul) which existed in a realm where there were perfect forms. In the world of forms there are perfect mathematical forms and perfect forms like the form of beauty and the form of justice.
We are born with a dim recollection of the forms because our soul apprehends them before becoming trapped in this world of appearances. Anamnesis is the process of re-remembering these forms through a posteriori sense experience.
Plato concluded that the source of knowledge must therefore be a priori, making him a rationalist
The consequence is that there must be a world of perfect and unchanging (immutable) forms, which he called the World of Forms. It is not a distant or other world – it is the true reality. What we see (the world of particulars/appearances) is not the true reality. Everything we experience is a vague shadow of what it really is; a perfect form.
P1. We have a concept of perfect justice and beauty and perfect mathematical concepts.
P2. We have never experienced perfect instances of such things.
C1. So, our knowledge of perfect concepts must be innate.
C2. Therefore there must be a world of forms and we must have a soul which gained perfect concepts from it before we were born.
Justice and beauty are subjective. We could deny P1 by arguing that beauty and morality are subjective; in the eye of the beholder. They seem like matters of opinion, not fact. It seems to be culture that determines and conditions what a person finds beautiful or just and as a result, views on what is beautiful or just change over time and differ cross-culturally. So, everyone has a different concept of perfect beauty or justice which makes it not objectively perfect.
Maths is not subjective. Perfect Plato’s examples of perfect circles and the idea of lines that are perfect equal can get around this issue, however. It is much harder to argue that mathematics is subjective.
Hume responds that we can actually create the idea of perfection in our minds even if we have never experienced it. We have take our concept of ‘imperfect’ and simply concieve of its negation: ‘not imperfect’ to gain the concept of ‘perfect’.
Furthermore we could add to Hume’s point that mathematical knowledge could come from experience. The slave boy may not have had any mathematical training, but he had seen shapes of objects in his life – thereby gaining concepts of shape and geometry from experience. This gave him a basic conceptual understanding that Socrates’ questioning brought out and clarified.
Finally, even if Plato was correct that we were born with perfect concepts, it doesn’t mean a soul and world of forms is the only or even best explanation. Evolution could have programmed us to have a sense of morality, beauty and the evolution of intelligence could explain being born with mathematical ability.
Aristotle: Plato’s theory lacks empirical validity
Aristotle thought the success of his theory of the four causes showed that Plato’s theory of forms was an unnecessary hypothesis, because it has no explanatory power regarding our experience. Plato’s forms are unchanging, but therefore cannot explain the change we experience in the world. This is like an early version of Ockham’s razor and is a general principle in empiricist epistemology: we should not believe explanations that are unnecessarily complicated, such as a world of forms, when we have a simpler theory that works. Aristotle concluded that the forms are “nonsense, and even if they do exist, they are wholly irrelevant”. Plato’s theory of forms lack empirical validity.
Aristotle does not reject the idea of form itself, but only the separation of form from things. On Aristotle’s view, a thing’s form or formal cause is its essence; its defining quality that makes it what it is. This also led Aristotle to reject Plato’s mind-body dualism, since the form of a human (rational thought) cannot be separated from their body.
Aristotle rejected the idea of the world of forms as lacking empirical validity, thus he also rejected the idea of some non-physical soul which could have come from such a world. Nonetheless, Aristotle still believes in the soul, but as the form of the physical body.
Form means essence, which is a thing’s defining characteristic. For a chair, its defining characteristic would be its shape, a shape that can be sat on. However, the essence of a human is not merely its shape. Aristotle claimed the defining feature of a human being is the ability to reason. Aristotle claimed that the soul was the formal cause of the body. He made an analogy with a stamp imprint in some wax. The imprint of the stamp has no actual positive existence separable from the wax, yet it nonetheless gives form to the wax. This is the relationship between the body and the soul for Aristotle.
Formal causation is unscientific. F. Bacon was called the father of empiricism for establishing the modern scientific method. He claimed that formal causation is a metaphysical matter that was beyond empiricial study. He gave the illustration of the ‘whiteness’ of snow and explained how science could investigate how snow results from air and water, but this only tells us about its efficient cause, not its colour, the form of ‘whiteness’, which is beyond scientific investigation. So Bacon thought that form existed, but Aristotle was wrong to think science could study it it.
Modern science goes much further than Bacon in its rejection of formal causation, arguing that we have no reason to think it exists at all. The idea that colour is a ‘formal cause’ of an object is now much better understood to be a matter of the activity of particles like atoms and photons, which can be fully explained through efficient and material causation. So what Aristotle thought of as ‘form’ actually reduces to material and efficient causation.
For Aristotle, the form of a human is a rational soul, but most neuroscientists would claim that rationality reduces to material brain structure and its physical processes. So again, what Aristotle thought of as ‘form’, actually reduces to material structure. There appears to be no room left in modern science for formal or final causation.
Science cannot currently explain how consciousness or reason reduces to material brain processes, however. The brain is so complicated and while some of it is understood a bit, processes like reason and consciousness have not even begun to be understood. So modern science cannot yet justifiably dismiss Aristotelian soul & form as the explanation of reason.
However, there is scientific evidence at least linking the brain to reason, since if the brain is damaged then reason and other mental faculties can be damaged too. Since there is so much about the brain we don’t understand, it’s more reasonable to think that mental faculties like reason are reducible to the material causation of brain processes in a way we don’t yet understand, rather than requiring some other type of physical explanation such as Aristotelian form since there is no evidence for that.
Descartes’ substance dualism
Descartes’ substance dualism is the theory that there are two distinct substances, mental and physical. A substance is a fundamental type of existence which can’t be broken down into anything else. The essence of mental substance is thinking, the essence of physical substance is extension. A thing is extended if it takes up physical space, is located, has coordinates.
Descartes’ indivisibility argument
Descartes argued that the essential property of physical substance is extension. Anything that is extended in space can be divided, because there has to be some point along which it could conceivably be divided. The mind does not appear to be divisible, however, because it seems to be non-extended. The mind is not located in space; it does not have spatial coordinates along which it could be divided.
Leibniz’ law is that identical things must have the same properties. The physical has the property of being divisible but the mental does not. If the body and mind were identical, then that one identical thing would be both divisible and indivisible, which is impossible. Therefore, the mind and body are not identical.
P1. Physical substance is divisible (since it’s extended).
P2. The mind is indivisible (since it’s non-extended).
P3. Leibniz’ law is that identical things must have the same properties.
C1. The mind therefore cannot be identical with any physical substance, such as the body.
The issue that the mental is divisible
The mental is divisible. The mind can be divided into perception, memory, emotions and so on. So, the mind and body share the same property of divisibility and thus could be identical.
This attacks P2, the premise that the mind is indivisible, in which case the mind does have the same properties as the physical body, making the indivisibility argument false.
Descartes responded that by the mind he means consciousness. Perception, memory and feeling are not divisions of consciousness, they are different modes of consciousness. It is the same undivided mind that perceives, remembers or feels emotions.
Divided hemispheres. Discoveries in modern science can be used to push the objection further and tackle Descartes’ account of the mind as consciousness head on. There are phenomena which have been discovered by modern psychology which could suggest that actual divisions of the mind are possible, e.g. blindsight & separated brain hemispheres. The brain is split into two hemispheres which are only connected by a thin strand of neurons called the corpus collosum, which can sometimes be cut as a medical procedure to treat epilepsy. This has the bizarre effect of, some have argued, seeming to result in two separate ‘persons’ in the one body. The right hemisphere controls the left arm and the left hemisphere the right arm. Patients have been observed picking up some food with one arm and the other arm hitting it away. One case involved a patient who tried to hug his wife with one arm and push her away with the other.
This is at least good evidence for the possibility of consciousness being divisible and gives us reason to think P2 false and the indivisibility argument therefore fails.
It also casts doubt on Descartes’ method in assuming that we have the full picture of what our mind is merely from how it seems to be to itself, which is his justification for P2.
The conceivability argument
P1. I have a clear and distinct idea of myself as a thinking non-extended thing.
P2. I have a clear and distinct idea of my body as a non-thinking extended thing.
C1. These opposing properties allow us to conceive of the mind separate to and without the body.
P3. What is conceivably separate is possibly separate.
P4. What is possibly separate is actually non-identical.
C2. Therefore, the mind and body are not identical.
Since the mind is non-extended, it is possible to conceive of it without any extended thing, existing independently of anything physical. For example, you could imagine being an immaterial ghost walking through walls.
If two things are actually identical, then they cannot possibly be separate. E.g., a triangle cannot possibly be sperate from having three sides. The separability of two identical things is not even conceivable. E.g., we cannot conceive of a triangle without three sides.
So, since we can conceive of the mind without the body it follows that it is possible for the mind to be separate from the body, from which it follows the mind is actually not identical to the body.
Masked man fallacy. Arguments reliant on inferring possibility from conceivability are susceptible to the masked man fallacy. Imagine someone heard about a masked man robbing a bank. They can conceive that it’s not their father, but if it really was their father then it’s impossible for it to not be their father, yet that was what they conceived. Therefore, we can conceive of the impossible. In that case, something’s being conceivable does not mean that it is possible.
This attacks P3, that what is conceivable is possible, by showing that we can conceive of the impossible.
The masked man fallacy only shows we can conceive of the impossible due to ignorance. The person in the example is ignorant of who is under the mark which is what allows them to conceive of the impossible. However, Descartes would argue that there is no analogous ignorance when it comes to our knowledge of our own mind. In the case of our mind, once properly understood through clear and distinct intellectual perception, there remains no ignorance that could lead to the conceiving of something impossible as happens in the masked bank robber case.
However, again Descartes assumes that the way the mind appears to the mind is how the mind actually is. He thinks that a clear and distinct intellectual perception of the mind shows us what it really is; a mental substance with the essential property of thinking.
Nonetheless, evidence from neuroscience and psychology shows us that we are ignorant about our mind in many respects. For example, most mental processing is unconscious and we are consciously unaware of the way in which our mind is influenced by it. This provides strong evidence against the view that the mind’s perception of itself is perfectly accurate let alone complete. So, it’s possible that we are ignorant about our minds and for all we know from out self-perception, our mind is extended and identical to our body. It follows that when we conceive of our minds as non-extended and thus separable from our body, it is possible that we are conceiving of the impossible due to our ignorance that our mind is our body.
So again, this defence against the relevance of the masked man fallacy begs the question by assuming that we know our mind is non-extended in order to prove that the mind is non-extended.
The interaction problem
This is a criticism of dualism. If dualism is correct and the mind and body are separate fundamental types of existence, how is it possible for them to interact? It seems that a mental desire to move a hand causes the bodily movement of the hand moving, and when the hand touches something hot it causes the mental feeling of heat. This requires non-physical mental substance to causally affect and interact with physical substance, but it’s not clear how that would be possible.
Princess Elizabeth of Bohemia argued that only physical things can interact with other physical things. She says interaction is when one thing pushes against another. A non-physical thing cannot do this. Therefore, if the mind is non-physical it cannot interact with the physical. However, it appears that the mental can cause the physical e.g my desire to touch a water bottle causes my arm to move and touch it. Therefore, dualism is false.
Descartes defence: Descartes tried to solve the interaction problem by suggesting that the mind and body interact at the pineal gland.
Counter-defence: There is no evidence or argument given in support of Descartes’ claim. He wrongly thought only humans had a pineal gland, but biologists later proved that false. More importantly, Descartes is saying where he thinks the mind and body interact, but the interaction problem doesn’t question where but how. Descartes is not providing an answer.
Furthermore, Physicists say that the universe is ‘causally closed’ because of the second law of thermodynamics that energy can be neither created nor destroyed – only transferred from one state to another. This means that energy cannot come from outside the physical universe and affect things within it. However that seems to be how substance dualism would have to work since the mental is supposedly outside the physical universe. Therefore substance dualism is false.
Gilbert Ryle & the category mistake
Ryle critiqued dualism, especially Descartes’ substance dualism:
“I shall often speak of it, with deliberate abusiveness, as “the dogma of the Ghost in the Machine“. I hope to prove that it is entirely false, and false not in detail but in principle. It is not merely an assemblage of particular mistakes. It is one big mistake and a mistake of a special kind. It is, namely, a category mistake.” – Ryle.
Ryle claimed Descartes was making a category mistake. Descartes says that physical things are extended, divisible and are non-thinking. He then argues that since the mind is non-extended, indivisible and thinking, it cannot be a physical thing and must therefore be a non-physical thing. Ryle argues that conclusion does not follow. Just because the mind is not a physical thing, that doesn’t mean it must be a non-physical thing. There could be another option – the mind might not be a ‘thing’ at all, of any type!
To illustrate why, Ryle told the story of someone being shown around a university. After they had been shown the various buildings, they then asked ‘but where is the university?’ They had mistakenly thought the university belonged to the category of ‘building’, rather than in the category of ‘a collection of buildings’.
To add another example, imagine someone asked ‘what is the taste of blue?’. That question involves a category mistake, thinking blue belongs to the category of things which have a taste.
Ryle argues that the language we use to describe the mind confuses us about the logical category it belongs to. We use the word ‘state’ and ‘process’ to describe physical things, but also use those words to describe mental terms. Since only physical ‘things’ can be in physical states or undergo physical processes, we thereby confuse ourselves into thinking that the mind must also be a ‘thing’ as it can be in mental states or undergo mental processes. Descartes, on the basis of that confusion, finds himself unable to locate a physical ‘thing’ that could be the mind and so wrongly concludes that it must be a non-physical thing – mental substance.
According to Ryle, Descartes baselessly assumes the mind is in the category of ‘things’ and when he finds that it’s not a physical thing he concludes it must be a mental thing. Ryle proposes another option, our word ‘mind’ does not refer to a thing at all, it actually refers to a sets of behavioural dispositions. Ryle is a philosophical behaviourist.
A disposition is a tendency for a thing to behave in a certain way under certain conditions. Ryle thinks that when we talk about the mind we are really talking about behavioural dispositions. For example if someone is described as scared, what is actually being described is their inclination, their disposition, to make scared facial expressions and run away.
Ryle illustrates this with the example of the “brittleness” of glass, which is the disposition of the glass to shatter upon impact. Is the brittleness of the glass a ‘thing’? Where is the brittleness of the glass? Does it have extension, can it be divided? Clearly the answer to such questions is no – just like Descartes answered to such questions when asked about the mind. But of course, we wouldn’t be tempted to draw the same conclusion about the brittleness of glass that we did for the mind. We wouldn’t be tempted by these questions to think of the brittleness of glass as being some kind of non-physical thing. So, Ryle concludes, nor should Descartes’ arguments tempt us to think of the mind as a non-physical thing either.
Criticism of Ryle: However, is the mind really a set of dispositions? Doesn’t it ‘feel like’ something to have a mind? Reducing the mind to a set of dispositions doesn’t seem to satisfactorily capture nor explain the fact that conscious awareness at least ‘feels’ like it ‘exists’ in some sense. It’s difficult to characterise that sense, but it seems overly reductionist and minimal to regard it merely as existing as dispositions to behaviours. Ryle was a philosophical behaviourist which is a controversial version of materialism.
Defence of Ryle: Ryle might be wrong that the mind is a set of dispositions, but he’s arguably still right to point out Descartes’ assumption that because the mind is not a physical thing, the only option is for it to be a non-physical thing. Who knows what other options there could be, aside from dispositions. Descartes’ conclusion at the very least requires much more justification than he gives.
Dawkins is a scientist and materialist. He argues that our current scientific view of what we are is that we are merely material physical beings composed of DNA. That’s all there is scientific evidence for, therefore we shouldn’t believe in anything supernatural such as a soul.
Dawkins argued there are two types of soul – one valid the other invalid. Soul 1 is the view that the soul is a real thing separate from our body, which Dawkins rejects due to lack of evidence. Soul 2 is a metaphorical idea of the soul, as a metaphor for the deep part of our mind and personality where the essence of our humanity is. For example, someone who doesn’t believe in a soul might still say “I felt that in my soul” or “Hitler was a soulless person”. They are just using the term ‘soul’ metaphorically for our deep important human feelings, not for some non-physical part of (soul 1). Dawkins thinks that everything about us, including our minds and consciousness, is nothing more than biological processes in our body and brain.
David Chalmers can be used to criticise Dawkins. Chalmers distinguishes between the ‘easy problem of consciousness’, which means figuring out which brain process is responsible for which mental process such as memory, perception or emotion, and the ‘hard problem of consciousness’, which is what brain process is responsible for consciousness itself. Chalmers points out that neuroscience has made progress as solving the easy problems of consciousness but has not come close to solving the hard problem. Chalmers recognizes the progress of neuroscience at solving the easy problem of consciousness but thinks that its failure thus far to make any significant progress at solving the hard problem suggests that explaining consciousness will require discovery of something new which is radically different to anything we currently understand. This could be a dualist mental property, but Chalmers admits it could also be a materialist physical property or thing we’ve not yet discovered. Our physical universe, once fully understood, could be just as far beyond our current conception as we are beyond Aristotle’s.
Defence of Dawkins: There are many things science cannot currently make much or any progress on, such as dark matter. This doesn’t give us grounds for supposing something non-physical might exist. We still have no evidence that anything non-physical exists.
Neuroscience is a young science and the brain is so incredibly complicated that it’s no surprise that no progress has been made on the hard problem of consciousness. That cannot be evidence for the possibility of science not being able to understand it because of it being a non-physical thing. In fact, since we know that there is so much about the physical structure of the brain that we don’t understand, arguably that should be a case for expecting the explanation of consciousness to be found once we gain more scientific understanding of the physical brain.
Plato’s cycle of opposites argument
P1. Every change from one state to another must involve a cycle of opposites. E.g. something becoming ‘smaller’ must be cycling away from ‘bigger’. A quality which has an opposite comes into being from its opposite.
P2. This cycling involves two opposite processes; e.g. increasing and decreasing. If these processes were not equally balanced, everything would be eternally getting bigger and bigger or smaller and smaller.
P3. Something dying is cycling away from the process of coming into life. Therefore, something coming into life must be cycling away from the process of death.
P4. This process must be balanced otherwise there would be only dead things or no dead things.
C1. There must be a soul which is cycling between life and death
Cycle of opposites criticism: Arguably ‘life’ and ‘death’ are not objective qualities but just descriptions of different arrangements of atoms. Objectively they cannot be opposites, therefore.
Arguably the universe is getting bigger and bigger, and has been doing so since the big bang, not for eternity. So Plato’s argument fails because he could not have been aware of the discoveries of modern physics.