The problem of other minds
The problem of other minds is an issue with dualism which is that if minds are non-physical substances or properties which cannot be reduced to physical properties then it looks like empirical science, which can only investigate the empirical, cannot grant us epistemic access to a mind. The only method left for gaining such access is introspection, however introspection can only grant knowledge of the mind of the person introspecting, not other minds. Therefore if dualism is true it seems impossible to ever know anything for sure about the minds of other people, including whether they even have one.
The argument from analogy response
Mill argues that he knows his mental states cause his behaviour and that other people have bodies which exhibit behaviours similar to his, by analogy he can infer that their behaviour has the same type of cause as his behaviour, namely mental states. So, other people have minds.
The one case response by N. Malcolm points out that the analogical arguer is making a generalization based only on one case; their mind.
A.J. Ayer attempted to improve the argument from analogy to avoid Malcolm’s objection. Instead of just the one case of my behaviour and my mind, we can note multiple links between multiple behaviours and multiple mental causes. We can then know, from our own experience, that many behaviours have a mental cause. Other people exhibit similar such behaviours, therefore those behaviour also have mental causes, so other people have minds.
However, although we have in our own introspective experience many cases of behaviours with a mental cause, they are all subsumed under the one case of our own mind.
We also know from our own experience that there are involuntary behaviours which do not have a mental cause, however, e.g. hiccupping. Induction to an alternative conclusion is therefore possible, that all the behaviour exhibited by others are of the involuntary sort.
Furthermore, as Hume points out regarding the teleological argument, like effects do not imply like causes. E.g. the different causes of fire and dry ice cause the same (like) effect of smoke.
The existence of other minds is the best hypothesis
The best hypothesis means inference to the best explanation. The best explanation of human behaviour is that it is caused by mental states; that they have minds. This is because it is the most metaphysically conservative and simple scenario. It’s hard to conceive of a simple reason why solipsism might be true. This is a scientific inference because it is an inference to the best explanation and doesn’t rely on private direct observation of private mental states, unlike the argument from analogy. This feature supposedly gets around Malcolm’s one case objection because it avoids relying on the one case of our own experience.
It’s metaphysically simpler if other people’s existence has the same degree/kind of explanation as my own existence. The idea that there’s something unique and special about us just seems to introduce metaphysical complexity.
How do we know that everyone having a mind is the simplest explanation? It might only seem that way because solipsism seems far-fetched to us. To assume solipsism is a more complex explanation is to assume we know about the metaphysics of what could cause solipsism to be the case, but we don’t.
Dualism makes a “category mistake” (Gilbert Ryle)
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 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.
The interaction problem
Dualist arguments do so much work to separate the mental from the physical, it opens up the question of how, then, it could be that they seem so connected and thus perhaps unseparated when they interact. E.g. I have a mental desire to move my hand and then my physical body moves. This seems to be the mind causing the body. How can two such radically different kinds of substance or property interact such that they can be in causal relationship? Conceptual problems for interaction are philosophical issues with conceptualising such interaction. Empirical problems for interaction are those raised by science.
The conceptual interaction problem (as articulated by Elisabeth, Princess of Bohemia)
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 responds by pointing to gravity. He claims that is an example of interaction with no pushing or touching of things. When I drop an apple, nothing pushes or pulls it. So therefore interaction with physical things doesn’t require pushing, as the princess supposed.
Modern Physics tells us that the atoms making up interacting objects don’t push or pull on each other, but the electrostatic force fields around the atoms are what do the pushing and pulling. Gravity is also an atom’s field of force which is much weaker in strength but extends much further in space. So Descartes was wrong to think that gravity doesn’t work in the same way as pushing or pulling.
Descartes also tried to solve the interaction problem by suggesting that the mind and body interact at the pineal gland.
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.
The empirical interaction problem
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.
What if, however, the total amount of energy passed into the universe by the mental causing the physical was equivalent to the energy passed out of the universe by the physical causing the mental? In that case the exact amount of energy would not change.
This response misunderstands the initial argument. It is not the total amount of energy which must be conserved according to the law of the conservation of energy, it is each individual unit of energy that can be neither created nor destroyed.
Epiphenomenalism is a form of dualism which is not susceptible to the interaction problem as it claims the mental and physical do not interact. It is the view that the physical causes the mental but the mental does not cause the physical. The mental is ‘causally inert’ or ‘causally inefficacious’.
The challenge posed by introspective self-knowledge
Introspection is the act of observing one’s own mind. We normally think that we can gain knowledge of the workings of our mind in this way, however if epiphenomenalism is true that appears to be impossible. For example, if I hit my foot on a chair and then, through introspection, notice that I am in pain, it appears that the mental state of pain has caused my belief that I am in pain. However, epiphenomenalism claims that mental states cannot cause anything. This goes against our experience.
It leads also to a deeper issue. If epiphenomenalism is true then the mental state of the feeling of pain and the mental state of the belief that I’m in pain must both have a physical cause which could possibly be two distinct physical causes. In that case, it is possible that the physical cause which caused my belief that I’m in pain might occur without the physical cause which causes the feeling of pain. This could be the case for every mental state which leads to radical scepticism about all of our knowledge of our own mind.
An epiphenomenalist could respond that this does not make their theory false.
The challenge posed by the phenomenology of our mental life
(ie as involving causal connections, both psychological and psycho-physical)
It appears to us that when I have a desire to touch my water bottle, my arm then goes out and touches it. Phenomenologically it feels like my mental state causes my physical body to move. It also feels like my mental state of, for example, repeating motivating mantras causes increased mental energy, focus and determination which would be a case of mental states causing other mental states. It is counter-intuitive to suggest that is not what is really happening.
What is counter-intuitive is no basis for an argument unless you grant the hidden premise that what we feel to be true must be true. Experiments from psychology have shown that what we are consciously aware of is a very superficial surface layer of an unconscious chasm of machinery we can’t consciously inspect.
The challenge posed by natural selection/evolution
Evolution by natural selection is the currently accepted scientific view. Epiphenomenalism has an implication which appears to conflict with it, which would mean that all the evidence for evolution would therefore count against the truth of epiphenomenalism. Natural selection means that the traits of an organism which give it a survival advantage are naturally selected for in the sense that those organisms with traits which confer less of a survival advantage are more likely to die and so less likely to pass on their genes. This suggests that only traits which confer survival advantage evolve. If the mind is causally inefficacious then by definition it cannot help an organism survive as it cannot cause anything. This means it cannot be naturally selected for and so cannot have evolved. The mind did evolve, therefore epiphenomenalism is false.
Consciousness could be a mere by-product of the superior intelligence that human brains have evolved. The intelligence certainly helps with survival and consciousness could simply be an epiphenomenon which, due to some undiscovered law of physics, is generated from a nervous system with sufficient complexity.