Materialist Theories of the Mind. Assimilate the mind, or eliminate it?

Transcription

1 Materialist Theories of the Mind Assimilate the mind, or eliminate it?

2 Materialist Theories of the Mind Functionalism A given mental state (e.g. pain) can be physically realised in many different ways. What s important is the functional role that state plays. The Identity Theory Each type of mental property is identical to a certain type of physical property. E.g. pain is just stimulation of the C-fibres. Eliminative Materialism Mental states like beliefs and desires do not exist. 2

3 The Identity Theory Ordinary mental concepts folk psychology will eventually be reduced to neuroscience. Each type of mental property (belief, pain, etc.) is identical to a certain type of physical property. Folk psychology (FP) is our common-sense theory of the mind. It explains peoples behaviour in terms of beliefs, desires, etc. 3

4 Type-type Reduction Many common-sense properties have been reduced to physics, i.e. shown to be identical to physical properties. E.g. Water is H 2 O Alcohol (ethanol) is C 2 H 5 OH Light is electromagnetic waves, between 400 and 760 nanometres in wavelength. Lightning is a stream of electrons Heat is molecular motion (kinetic energy)

5 Type-type Reduction And so (no doubt) we ll someday discover such things as: Belief that the earth is round is neural configuration FS273.4 in the temporal lobe of the left cerebral hemisphere. A sharp toothache is activation state A-D of the anterior cingulate cortex. 5

6 Folk psychology A typical example of a folk psychological generalization would be: If someone has the desire for X and the belief that the best way to get X is by doing Y, then (barring certain conditions) that person will tend to do Y. (Stanford Encyclopedia of Philosophy, entry Eliminative Materialism )

7 The Identity Theory [The identity theory] claims that neuroscience will discover a taxonomy of neural states that stand in one-one correspondence with the mental states of our common-sense taxonomy. (p. 317) (Churchland regards this as unlikely) 7

8 Martian Pain Churchland finds the martians argument against the identity theory very persuasive. This argument is used by functionalists to attack the identity theory. 8

9 Imagine a being from another planet, says the functionalist, a being with an alien physiological constitution, a constitution based on the element silicon, for example, instead of the element carbon, as ours is. (p. 321) joy-in-a-human = resonances in the lateral hypothalmus Whereas Joy-in-a-Martian = something else entirely (p. 324) 9

10 In other words, the identity theory is attacked by the argument that Martians (if they exist) will have mental states analogous to joy, pain, etc. These states will have similar functional roles to ours. But quite likely a different physical basis. So mental states like joy, pain etc. are really functional states, not physical ones. 10

11 Functionalists thus reject the (type-type) identity theory, that each type of mental state is identical to a type of physical state. However, functionalists generally accept a token-token identity theory, that: each instance of a given type of mental state is numerically identical with some specific physical state in some physical system or other. (p. 322) 11

12 Churchland defends functionalism While not a functionalist, Churchland defends functionalism from some of the criticisms we considered earlier. E.g. the inverted spectrum argument. Churchland suggests that, even if we have different experiences of red objects, we are still in the same mental state of sensation of red. 12

13 Churchland suggests that the experience (quale) of red may in fact be a physical (not functional) state. If the pitch of a sound can turn out to be the frequency of an oscillation in air pressure, there is no reason why the quale of a sensation cannot turn out to be, say, a spiking frequency in a certain neural pathway. (p. 323) 13

14 Eliminative Materialism Eliminative materialism says that concepts from folk psychology, e.g. beliefs and desires, should be eliminated. Other eliminated concepts include the celestial spheres, phlogiston, the life force, the ether, demon possessions, etc. Will science ultimately conclude that beliefs, like demon possessions, don t exist? 14

15 Why eliminate folk psychology? Folk psychology is a failure. We don t understand sleep, learning, intelligence, memory. The theory is stagnant. No progress in over 2,000 years. FP is especially hopeless at understanding damaged brains (mental illness). All other folk theories turned out to be radically false (nature of fire, life, )

16 Is eliminativism about beliefs incoherent, or self defeating? Say, Paul, do you believe that eliminative materialism is correct? Yes, as a matter of fact I do. Aha! So beliefs do exist!! 16

17 A self-defeating claim Science tells us that there is no such thing as human knowledge.

18 Churchland s Response The hole in this argument is the premise concerning the conditions necessary for a statement to be meaningful. It begs the question. If eliminative materialism is true, then meaningfulness must have some different source. (p. 328)

19 The full argument 1. We eliminative materialists (EMs) go around saying things like folk psychology is a radically false theory and should be discarded. 2. Eliminative materialism (EM) is true. 3. A sentence is meaningful only when it expresses a proposition, or belief-content There are no beliefs, or propositions (from 2) 5. Sentences expressing EM have no meaning (3 and 4) 6. When we EMs try to convince others to accept EM, our words have no meaning, and are just noise. (from 1, 5) 19

20 In response, Churchland says that sentences can be meaningful without expressing beliefs. But it s hard to see what this notion might be replaced with. At the very least, Churchland has a lot of work to do here, redoing all of logic as well as psychology. (N.B. Logic studies propositions, which are belief-contents.)

21 Churchland says that similar arguments could be made to show that eliminativism about the other discarded notions, such as the life force, are also incoherent. Are the cases similar?

22 My learned friend has stated that there is no such thing as a vital spirit. But this statement is incoherent. For if it is true, then my friend does not have a vital spirit and must therefore be dead. But if he is dead, then his statement is just a string of noises, devoid of meaning or truth (Churchland p. 328)

23 Vitalism doesn t seem necessary to our understanding of what thought, truth, etc. are. But the concept of belief does seem essential. If there are no beliefs, then there are no states of affairs, no truth, etc. Yet the whole idea of science is to construct models that accurately correspond to reality (i.e. are true). Can science end up eliminating the concept of truth itself? Dualists will no doubt listen to Churchland with glee, saying that materialism leads, in the end, to irrationality.

24 Self-defeating views In philosophy there are a surprising number of views that turn out to be self-defeating, or self-referentially incoherent. -- At least, this criticism is made against them. 24

25 Locke on perceptual scepticism I think nobody can, in earnest, be so sceptical as to be uncertain of the existence of those things which he sees and feels. At least, he that can doubt so far (whatever he may have with his own thoughts), will never have any controversy with me; since he can never be sure I say anything contrary to his own opinion Ha! Nice one, J.L.

26 In other words Sceptic: Hey John, I don t agree with your claim that our senses provide us with knowledge. JL: How do you know I said that? Sceptic: I just heard you, loud and clear! JL: Aha! You learned it from your senses!

27 Another example Professor: All interpretations of a text are equally valid. The author s intention is a myth. Student: Ah, very amusing, professor. I love the sarcasm, the way that you mock the view, while appearing to support it. Professor: No, no. You misunderstood me. I was being serious! Student: Hilarious! Keep the sarcasm going! (Etc.)

28 The Verifiability Criterion of Meaning The verifiability criterion of meaning says that, in order to be meaningful, a statement must be empirically verifiable. There must be experimental conditions under which the statement can be shown to be true. (E.g. God is love is meaningless.) Karl Popper: the criterion itself is not empirically verifiable, and hence is meaningless by its own lights.

29 Classical Foundationalism Classical foundationalism says that, in order for a belief to count as knowledge, it must be either (i) self evident, or (ii) logically derivable from self evident beliefs. Alvin Plantinga: Classical foundationalism itself isn t self evident. Nor can it be derived from such self evident beliefs