- Essential reading – 75
- Further reading – 75
- Introduction – 75
- Kripke's conceivability argument – 75
- Objections – 78
- Jackson's knowledge argument – 79
- Objections – 79
- Conclusion – 80
- Learning outcomes – 80
- Sample examination questions – 81
- Tips on answering the sample questions – 81
- Essential Reading
- Further reading
- There is a criticism of identity theory which needs to be examined in detail because, although it is a bit tricky and technical, it
… is a very powerful criticism
… raises issues which are very important about the tools and methods of philosophical enquiry and what can be accomplished with them.
- This is Kripke's Conceivability Argument. This argues that to reduce mental states to nothing but brain/central nervous system states is inescapably to be committed to a very strong identity (necessary identity) which even the materialist neither wants nor accepts.
- A second criticism, Frank Jackson's Knowledge Argument, threatens not just the identity theory but any sort of materialism from behaviourism to anomalous monism because it suggests that they all leave out something crucial. They leave out the felt quality of experience, the subjective nature of mental states which can be known although only by the subject himself. Since there is more to be known about the mental than would be provided by even a completed physical science, there is more to reality than the realm ranged over by the physical sciences.
- Kripke's conceivability argument
- Kripke's overall strategy can be briefly, if cryptically, stated:
… Show that identity cannot be contingent.
… Show the identity theorist that this means he or she has the task of defending the necessity of mind/brain identity.
… Explain why the identity of mind and brain cannot be defended as necessary.
- Identity cannot be contingent
- Kripke is an essentialist about mind and body — that is, he thinks that there are, in mind and body themselves, independently of our interpretation of each sort of thing, features essential to being a mind or, alternatively, to being a body.
- Bodies for Kripke are, of their very essence, public and spatial — they are accessible in principle to any observer and they have length, breadth and height. However minimally, they take up room.
- Minds, by their very nature, are private, knowable directly only by introspection, and non-spatial. They take up no room and have no spatial location. The properties which it would be logically possible or impossible for mental phenomena to possess differ markedly from those it would be logically possible or impossible for physical phenomena to possess.
- But if all these apparently highly plausible claims about mind and body are true, Kripke maintains, it cannot be right to claim an identity between mind and body, mental states and brain states. Surely, as we have just seen, the two things are essentially different.
- The rebuttal which the early identity theorists had to hand was that they had never claimed that the identity of, say, pain with c-fibre firing (a physical, brain state) was anything other than a contingent identity1 — one that need not have been true, one that just happened to be true. They were certainly not claiming that ‘in pain' had the same meaning as ‘in a c-fibre firing state'.
- Of course, to take an analogy, water and H2O have different essential properties - water is a clear, colourless, thirst-quenching liquid and H2O is a compound of hydrogen and oxygen in certain proportions. The two symbols (‘water' and 'H2O') have different meanings and we can easily imagine a world in which the prevalent clear, thirst-quenching liquid is not H2O. Water and H2O are contingently identical, the identity theorist says, and so too with mind and body.
- Kripke's reply is that there is no such thing as ‘contingent identity2'. If you think about what identity, strictly speaking, is you will see that Kripke is saying something with a great deal of intuitive force. If a thing known under one description (say ‘water') is correctly said to be identical with something known under a different description (say, 'H2O') what is being said is that there are, not two things, but one: something is identical with itself!
- How could this be anything but a necessary truth — one that is true whatever the circumstances, come what may? Surely the proposition that states that ‘a thing is identical with itself' must be as unalterable and inevitable (necessary) as a proposition can get. Try imagining what you would have to do to a thing to make it stop being identical with itself. The very idea is nonsensical.
- If mind and brain are identical then the identity is necessary
- So the first part of Kripke's strategy — to force the identity theorist to realise that necessary identity is the only kind of identity — should be fairly readily accomplished. But why had the identity theorists ever thought it was right to describe the identity of mental states and brain states as ‘contingent'? They were persuaded that brain state/mental state identity would turn out to be another in the long line of scientific intertheoretic reductions, identifications between such things as water and H2O or heat and mean molecular motion. It seemed to them that for all these identifications there was an element of happenstance somewhere along the way.
- What is meant by ‘happenstance' here? Well, it seemed easy to conceive of how, given a different set of surroundings in another part of the universe or given a different history of development of nature since the Big Bang, there could have developed quite different identities. Why couldn't a quite different compound with a quite different chemistry be the liquid that strikes our senses as water does and serves the same role in our world and life (falls out of the sky as rain, fills the oceans, etc). And why couldn't a quite different molecular property be the one to cause us to feel hot (sense heat) when we came near what had that property (as we now do when we come near something whose molecules are in rapid motion)?
- To this Kripke responds by saying, roughly, ‘think what you are actually imagining or conceiving when you think that the identity between water and H2O is only contingent and could have been different'. You aren't imagining water, that very substance which in fact has the hydrogen and oxygen composition with which chemists are familiar, being somehow chemically different while still being water. You are, instead, imagining a wholly different world without water and with a different substance which fulfils the same roles, looks like our water, tastes like it, etc. (perhaps even gets called ‘water') but is not water.
- Kripke invents the term ‘rigid designator' for words like ‘water' in the last paragraph — words that pick out the self-same, unique thing in all conceivable circumstances (as it is sometimes said ‘in all possible worlds'). The term ‘water' designates stuff that happens to have the chemical constitution H2O but the identity of what it designates with itself (with what it designates!) is a necessary truth and nothing but. Not only ‘water' but also 'H2O' is a rigid designator and ‘water is (identical with) H2O' is a necessary truth even though we must find out truths like ‘water is H2O' by empirical research. (We don't know it a priori, independently of experience.)
- The mind/brain identity thesis cannot be defended as a necessary identity
- If holders of the identity theory are defending the truth of ‘mental states are brain states', ‘mind = brain', they must defend them as what they are, necessary truths. How do you defend a truth as necessary? At last this is where conceivability comes to the fore. A necessary truth, remember, is one that is not just true but cannot conceivably be false — it is true come what may, in all possible worlds, in all conceivable circumstances.
- So one way to prove, or at least support, a necessary truth as necessary is to look at the conceivability of its opposite or find a counter instance. If none can be found (and if we can explain why not), then this lends strong support to the claim that the original proposition or statement is, as originally suspected, not just true but necessarily true.
- By the same token, if you wonder whether a proposition which has been claimed to be necessary may not possibly fail to be necessary despite that claim, you could ask yourself whether you can conceive of that proposition's being false after all. Consider the stock example, ‘pain is (identical with) c-fibre firing'. Can you conceive of pain that is not c-fibre firing? Kripke's answer to this is, ‘Yes, of course you can'. Suppose you have a headache and, at the same time, your c-fibres are firing. You can conceive of (imagine) someone who has completely different brain events occurring in his brain (no c-fibre firing) and yet has a headache with exactly the same painful quality yours has.
- You can also, Kripke says, imagine your exact molecule-for-molecule double having the same sort of c-fibre firing as you have but feeling no pain whatsoever. So ‘pain is c-fibre firing' is not a necessary truth. But Kripke has argued that all true identities are necessary. So, if the proposition isn't necessary, it isn't even true.
- How is it, on Kripke's view, that we can imagine a world where something exists that looks, feels, tastes, etc. just like water (= H2O) but there is no water (= H2O) in that world when, according to him, there is no conceivable world where something that feels exactly like pain exists but no (genuine) pain exists? The answer is simply that pain (the phenomenon itself) cannot be distinguished from the sensation or feeling (or appearance) of pain. Thus, there cannot be a distinction between how it appears or is sensed to be and how it really is. If it hurts it is pain; if it doesn't, it isn't. There is no room for something that is pain but isn't felt or something that isn't pain although it hurts.
- This conceivability argument is very difficult to keep steadily clear about. If you want to understand and write on it in the exam, you will need to repeat the main steps in the argument again and again. Look at the outline of the argument at the beginning of the chapter. The important point is that identity can only be necessary: there is no half-way house. A contingent statement like ‘heat has turned out to be mean molecular motion' is not an identity statement. It is not, as identity statements are, a variant on the proposition ‘a thing is itself' (in this case ‘heat is heat").
- It can be used to say either ‘this is what we have found out after long research: "heat is mean molecular motion" is a true (necessary) identity' or something like ‘in this (actual) world, with chemistry as we know it, what causes sensations of heat is, as a matter of fact, (necessarily) identical with mean molecular motion'. We could have elected to call something else ‘heat', but what we now call ‘heat' could not remain that very individual phenomenon it is (with the nature it has) and also have a different nature.
- Objections: Critics have raised three objections to Kripke's argument:
- The first is a general worry about the status, scope and limits of conceivability and thought experiments3 in philosophy. What can be learned or safely concluded from thinking about what we do or do not find ourselves able to conceive or imagine? Does it matter who does or tries to do the conceiving? If I cannot imagine something or other, does this prove the impossibility of the existence or occurrence of what I failed to imagine? Are there some minds that can conceive more and better possibilities than others?
- If you do as Kripke asks and try to conceive the very mental state in which you are now being had by someone else or by yourself although your brain state is entirely different, how will you tell whether what you have conceived is that very, self-same, token mental state in different physical circumstances or a (numerically different) mental state exactly, qualitatively similar to the original? Is there any difference between the suggestions? (See "Carruthers (Peter) - Introducing Persons: Theories and Arguments in the Philosophy of Mind", pp. 151-55.) Since Kripke's purpose is to show that mental states and physical states cannot be identical because they have essentially different natures and could conceivably enjoy different fates, this criticism of Carruthers' is very well taken. Perhaps I cannot imagine this very (present token) mental state occurring in any other circumstances. Perhaps every attempt fails and all I manage is to conceive an exactly similar replica mental state which would prove nothing about whether the original mental state and its associated brain state are one entity or two.
- Some critics concede that Kripke has defeated type—type identity theory (discussed in Chapter 7), but feel that token identity remains undefeated. Could this very mental state really exist in the absence of my present brain state? Could this token brain state I am now in exist though my mind was enjoying a quite different mental state? Does my ability in each case to conceive one without the other (supposing I can) prove that this mental state and this brain state are not identical with each other?
- Jackson's knowledge argument
- Before I begin talking about this argument, I ought to say that Frank Jackson now says that he no longer believes its conclusion. However, there are two good reasons for persisting in learning about it despite its author's change of heart. First, it has been a hugely influential argument in the philosophy of mind over the last fifteen or so years and many have been persuaded by it (and a similar position found in "Nagel (Thomas) - What is it Like to Be a Bat?", p. 127) that ‘the material or physical story about us is not the complete story about us'.
- The second reason is, of course, that his argument may have been right and it may be his second thoughts that are wrong!
- If you look at "Graham (George) - Philosophy of Mind: An Introduction" (pp. 10-11), you will find a clear, brief version of Jackson's tale about Mary, the brilliant neuroscientist who has spent her whole life imprisoned in a wholly black and white environment learning everything there is to know about the science of colour vision. Supposing that all science is available to her (this story is set in the future after all the sciences have been made complete), it seems that Mary will still not know all there is to know about colour vision until she is released from her prison in order to have the colour experiences which can give her knowledge of what, for example, seeing red feels like. This fact about colour experience is beyond the preserve of physical science: there is still something for experience to teach after Mary has learned all that science contains on this subject.
- The language reply
- Learning (for example) the colour vocabulary (as Mary does when she escapes the black and white environment) is just a case of her learning to express what she already knows in different terms. It is as if she were learning a new natural language when she sees her first ripe tomato, but Mary does not really learn anything new.
- The natural reply to this objection is that no one imagines that this view captures how Mary is likely to feel and speak about her knowledge. She will not feel that she has merely learned some new words to express what she already knew all along. She will feel that she has learned something new about reality from her new experience — that ‘seeing red feels like this'.
- The different perspectives reply
- Another objection says that the knowledge argument overlooks an important point about knowledge in general — namely, that you can know all about a particular thing or happening from one angle while failing to know the same things from a different angle. Remember the example of the ineffectual speaker whose words are easy to doubt until I find out that he is the scientific expert I already respect (Chapter 2 above)? Knowledge is much like doubt in this regard. Mary could know that people whose eyes are receiving light waves of such and such a description will have brain states like this or that, without knowing that this is ‘sensing red' in those people.
- The reply to this objection is that Mary is not in the position it envisages. She is not unaware that sensing red is being in such and such a brain state. Until her release she simply does not know what sensing red is like or feels like.
- The know-how reply
- Finally, there are a number of objections to the knowledge argument which say that Mary may learn something from her first sensory encounter with red things, but it is not new factual knowledge she acquires. Instead, she learns how to do something. She now has a recognitional capacity she lacked before: she can recognise red things as such straight off, without using scientific machinery to measure the wavelengths of light reflected from their surfaces or anything of the sort. She knows red on sight, but she does not have any new factual knowledge about the world.
- This last objection (associated with the names Nemirow, Mellor and Lewis) strikes some readers as a perfect compromise solution and strikes others as a mere verbal quibble — call it ‘factual knowledge' or just ‘a new recognitional capacity', Mary seems to have something new after seeing red for the first time and it seems that that something new is not something physical.
- The dualist and materialist accounts of the mind that have been surveyed in Chapters 1 to 9 of this guide cover, or at least touch on, all the major points of view which have emerged from Plato's time to the present about the fundamental (metaphysical) nature of persons — subjects of experience, such as you and me. The main point of contention has been the question whether or not physical substances obeying physical laws are the only sort of substances (and) laws involved in the existence of persons - the paradigm cases of beings with minds.
- Some people believe that a two substance theory can overcome even the very powerful objections to substance dualism outlined in Chapters 1-4. Others are persuaded that a materialist monism (a single physical substance theory) of some sort would give the only correct account of the nature of minded subjects/persons. Finally, we have seen that the materialisms of various sorts we have examined also face some formidable difficulties:
- They are accused of leaving the mental with no power to influence action (an objection directed at Davidson).
- They are said to fail to take account of a significant part of our knowledge as experiencing subjects — namely, our knowledge of the qualitative character of experience (an objection raised by Jackson and Nagel).
- The conceivability argument seems to rule out any straightforward identity between the physical and the mental so the materialist must, at least, forswear the crudest forms of reductionism (an objection raised by Kripke).
- It may be that there are no substances which are anything other than physical, but mental properties emerge from or supervene4 upon the physical and are not reducible to physical properties.
- Learning outcomes
- After completing this chapter and reading the recommended pages and chapters, you should be able to:
… State Kripke's conceivability argument, breaking it down into its premises and showing how the conclusion depends on the premises.
… Summarise Jackson's knowledge argument in the same careful and detailed way.
… Outline and explain the force of three objections to each argument.
- Sample examination questions
- ‘I can conceive of having this very thought though my present brain and whole body did not exist.' Can a successful argument against materialism be based on a claim about what can be imagined?
- ‘When I first see a colour I have in fact never seen before in my whole life, do I acquire a new piece of knowledge?' How is materialism about the mind threatened by a ‘yes' answer to this question?
- Tips on answering the sample questions
- A successful answer to each of these questions would start by showing that you recognise which philosopher's view is being discussed (Kripke first, then Jackson). Who are the opponents addressed by each of the philosophers named?
Part 1 (The Metaphysics of Mind and Body); Section 2 (Varieties of anti-dualism and materialism); Chapter 9. Hard Copy filed in "Various - Papers on Religion Boxes (Heythrop)"
Text Colour Conventions (see disclaimer)
- Blue: Text by me; © Theo Todman, 2018
- Mauve: Text by correspondent(s) or other author(s); © the author(s)