Philosophy of Mind Matthew Soteriou

Physicalism The physicalist answer to the question of the relation between the mental and the physical: The mental is physical.

Identity Theories According to identity theories: the ‘is’ here is the ‘is’ of identity. E.g. the relation between the mental and physical (or mental state and brain state, or mental event and physical event) is one of identity.

First point in defence of the claim is that identity statements can be informative. That a=b can be an empirical discovery. E.g. it was an empirical discovery that water is H2O

The Type-Token Distinction The distinction between a type and its tokens is an ontological one between a general sort of thing and its particular concrete instances.

Token physicalism: For every actual particular (object, event) x, there is some physical particular y such that x = y.

Type Identity physicalism: According to Type-Identity physicalism types of mental states / events are identical to types of physical states / events. Often taken to be a property-identity theory: for every actually instantiated mental property F, there is some physical property G such that F=G.

Is token physicalism consistent with dualism? As we shall see, there are versions of token physicalism that rule out certain versions of property dualism. The debate between these token identity phsycailists and property dualists turn on whether the menal ‘supervenes on the physical’.

Reductive physicalism: One very strong form of reductionist thesis is a conceptual reductionist view, according to which for each mental predicate F, there is a physical predicate G such that a sentence of the form ‘ x is F iff x is G’ is analytically true.

Reductive physicalism: A weaker reductionsist view: The properties expressed by the predicates of a psychological theory are identical to the properties expressed by the predicates of a neurological theory. This version of reductionism is a version of type identity physicalism.

David Lewis’ argument for type identity. My argument is this: (1) The definitive characteristic of any (sort of) experience as such is its causal role, its syndrome of most typical causes and effects. But we materialists believe that (2) these causal roles which belong by analytic necessity to experiences belong in fact to certain physical states. (3) Since these physical states possess the definitive character of experiences, they must be experiences. (Lewis, 1966)

The first premise of the argument: The definitive characteristic of any (sort of) experience as such is its causal role, its syndrome of most typical causes and effects. Lewis offers a recipe for the analysis of mental states in terms of their causal roles. Note that according to Lewis the causal roles of mental states involve other mental states.

Is there something problematically circular about analysing mental states in terms of other mental states if you are a materialist?

The solution: ‘Ramseyfication’ of our psychological theory. F.P. Ramsey had shown how to replace the theoretical terms of a theory such as ‘the property of being an electron’ by ‘the property X such that...’ so that when this is done for all the theoretical terms, we are left only with ‘property X such that’, ‘property Y such that’ etc. Take the terms describing behaviour as the observation terms and psychological terms as the theoretical terms of ‘folk’ psychology. Then, the suggestion is, Ramseyfication shows that folk psychology is compatible with physicalism.

The second premise of Lewis’ argument: “These causal roles which belong by analytic necessity to experiences belong in fact to certain physical states.” Is this just supposed to be a plausible empirical claim? Is the claim justified by the completeness of physics?

The argument for the Identity Theory: (1) Mental state M = the occupant of the M-role (by analysis) (2) Physical state P = the occupant of the M-role (by science). Therefore (3) M = P

Example: Pains are the kind of thing that typically have such-and- such physical causes and such-and-such physical effects, where the ‘such-and-such's are filled in by our folk theory of pain. Since the physical is causally closed, the things that have such-and-such physical causes and such-and-such physical effects are themselves physical. So, pains are physical

For any particular case we can in principle discover the relevant identity. E.g. – Pains are the kind of thing that typically have such-and-such physical causes and such-and-such physical effects, where the ‘such-and-suches’ are filled in by our folk theory of pain. – Neural state N is the state that has such-and-such physical causes and such-and-such physical effects. – So, pains are instances of neural state N.

According to Lewis mental states are contingently identical with physical states. “If M means ‘the occupant of the M-role’, it’s contingent which state is the referent of M: it’s contingent whether some one state is the referent of M and P; so it’s contingent whether M = P is true”.

Mental Causation Consider again the causal argument for physicalism introduced last week: 1. Mental events cause physical events 2. Completeness of physics 3. No overdetermination Solution: Mental events are physical events. A question we might then ask: Do these mental events cause their physical effects in virtue of their mental properties, or their physical properties?

Mental Causation A virtue of the type identity theory is that it can accommodate mental causation in a straightforward way. The type identity theorist can say that mental events cause physical effects in virtue of their mental properties, while consistently maintaining that such physical effects can be causally explained in physical terms. For they can maintain that the mental properties in question are identical with certain physical properties.

Multiple Realizability Objection to the Type Identity Theory The multiple realizability thesis: a single mental kind can be realized by many distinct physical kinds. A common example often cited is pain. Putnam argues that there are a wide variety of terrestrial creatures seemingly capable of experiencing pain. E.g. humans, other primates, other mammals, birds, reptiles, amphibians. But is there really some physical-chemical kind common to this wide variety of pain-bearing species, and correlated exactly with each occurrence of the mental kind?

This thesis is often presented as an objection against theories that identify mental states with brain states. The Objection: (1) Mental kinds are multiply realizable by distinct physical kinds. (2) If a given mental kind is multiply realizable by distinct physical kinds, then it cannot be identical to any specific physical kind. Therefore, (3) No mental kind is identical to any specific physical kind.

Is the MRT an empirical claim? Could there be an a priori argument for the thesis? A point we’ll return when we consider Davidson’s arguments for the “anomalism” of the mental.

Lewis’ Response: David Lewis argues that the apparent inconsistency between the reductionist's type identity theory and multiple realizability is only apparent. We need to keep in mind the way in which the type identity claims are relative to contexts.

Illustrative example The following three claims appear inconsistent: (1) There is only one winning lottery number. (2) The winning lottery number is 28. (3) The winning lottery number is 61.

Now append “per week” to (1), “this week” to (2), and “last week” to (3). (1) There is only one winning lottery number per week. (2) The winning lottery number this week is 28. (3) The winning lottery number last week is 61. There is no inconsistency.

These three similar claims likewise seem inconsistent: (1′) (the reductionist thesis) There is only one physical-chemical realization of pain. (2′) The physical-chemical realization of pain is C-fiber firing. (3′) The physical-chemical realization of pain is … (something else – e.g. D-fiber firing.

But now append “per structure-type” to (1′), “in humans” to (2′), and “in reptiles” to (3′). (1′) (the reductionist thesis) There is only one physical-chemical realization of pain per structure type. (2′) The physical-chemical realization of pain in humans is C-fiber firing. (3′) The physical-chemical realization of pain in repitles is D-fiber firing. Lewis's point is that reductive identities are always specific to a domain.

“If M means ‘the occupant of the M-role’ and there is variation in what occupies the M-role, then our psychophysical identities need to be restricted: not plain M = P, but M-in-K = P, where K is a kind within which P occupies the M role.” (E.g. Pain-in-humans).

Further responses to the multiple realizability objection: Is it really so obvious that the same functional characterization can be given of ‘pain’ across different species? (Note that scepticism about this might lead one to question whether the question Lewis is right to think that it is possible to analyze the causal role played by any given mental state independently of careful empirical investigation.)

Too much “local reduction” seems inconsistent with the assumed generality of science. The type identity theory will only be plausible if we can establish type identity claims at an appropriate level of generality. But some argue that it remains open that such type-identity claims can be established. The thesis has not yet been empirically ruled out.

Further questions: Are there some mental properties that seem more likely than others to be candidates for establishing type identity claims? Think of the variety of different aspects of mind: Beliefs, desires, wishes, thoughts… Sensations, perceptual experiences, emotions…

Note that some suggest that sensational/phenomenal properties of our conscious mental states may be the likeliest candidates for which type identity claims can be established. Yet some think that sensational/phenomenal aspects of mind are the least likely to be physical.