See the discussion. of content externalism below.) One objection to this view, due to Ned Block, is that it would mistakenly count as an intentional agent a giant look-up table – ‘a Blockhead’ – that has the same dispositions to peripheral behavior as a genuine intentional agent. (A look-up table is a simple mechanical device that looks up preprogrammed responses.)
Identity theories. In the early 1950s, Herbert Feigl claimed that mental states are brain states. He pointed out that if mental properties or state types are merely nomologically correlated with physical properties or state types, the connecting laws would be ‘nomological danglers’: irreducible to physical laws, and thus additional fundamental laws. According to the identity theory, the connecting laws are not fundamental laws (and so not nomological danglers) since they can be explained by identifying the mental and physical properties in question. In the late 1950s and the early 1960s, the philosopher Smart and the psychologist U. T. Place defended the materialist view that sensations are identical with brain processes. Smart claimed that while mental terms differ in meaning from physical terms, scientific investigation reveals that they have the same referents as certain physical terms. (Compare the fact that while ‘the Morning Star’ and ‘the Evening Star’ differ in meaning empirical investigation reveals the same referent: Venus.) Smart and Place claimed that feeling pain, e.g., is some brain process, exactly which one to be determined by scientific investigation. Smart claimed that sensation talk is paraphraseable in topic-neutral terms; i.e., in terms that leave open whether sensational properties are mental or physical. ‘I have an orange afterimage’ is paraphraseable (roughly) as: ‘There is something going on like what is going on when I have my eyes open, am awake, and there is an orange illuminated in good light in front of me, i.e., when I really see an orange’. The description is topic-neutral since it leaves open whether what is going on is mental or physical. Smart maintained that scientific investigation reveals that what in fact meets the topic-neutral description is a brain process. He held that psychophysical identity statements such as ‘Pain is C-fiber firing’ are contingent, likening these to, e.g., ‘Lightning is electrical discharge’, which is contingent and knowable only through empirical investigation. Central state materialism. This brand of materialism was defended in the late 1960s and the early 1970s by Armstrong and others. On this view, mental states are states that are apt to produce a certain range of behavior. Central state materialists maintain that scientific investigation reveals that such states are states of the central nervous system, and thus that mental states are contingently identical with states of the central nervous system. Unlike logical behaviorism, central state materialism does not imply that mental sentences can be translated into physical sentences. Unlike both logical behaviorism and intentional systems theory, central state materialism implies that mental states are actual internal states with causal effects. And unlike Cartesian interactionism, it holds that psychophysical interaction is just physical causal interaction.
Some central state materialists held in addition that the mind is the brain. However, if the mind were the brain, every change in the brain would be a change in the mind; and that seems false: not every little brain change amounts to a change of mind. Indeed, the mind ceases to exist when brain death occurs, while the brain continues to exist. The moral that most materialists nowadays draw from such considerations is that the mind is not any physical substance, since it is not a substance of any sort. To have a mind is not to possess a special substance, but rather to have certain capacities – to think, feel, etc. To that extent, Ryle was right. However, central state materialists insist that the properly functioning brain is the material seat of mental capacities, that the exercise of mental capacities consists of brain processes, and that mental states are brain states that can produce behavior.
Epistemological objections have been raised to identity theories. As self-conscious beings, we have a kind of privileged access to our own mental states. The exact avenue of privileged access, whether it is introspection or not, is controversial. But it has seemed to many philosophers that our access to our own mental states is privileged in being open only to us, whereas we lack any privileged access to the states of our central nervous systems. We come to know about central nervous system states in the same way we come to know about the central nervous system states of others. So, against central state materialism and the identity theory, it is claimed that mental states cannot be states of our central nervous systems.
Taking privileged access to imply that we have incorrigible knowledge of our conscious mental states, and despairing of squaring privileged access so understood with materialism, Rorty advocated eliminative materialism, the thesis that there actually are no mental phenomena. A more common materialist response, however, is to deny that privileged access entails incorrigibility and to maintain that privileged access is compatible with materialism. Some materialists maintain that while certain types of mental states (e.g., sensations) are types of neurological states, it will be knowable only by empirical investigation that they are. Suppose pain is a neural state N. It will be only a posteriori knowable that pain is N. Via the avenue of privileged access, one comes to believe that one is in a pain state, but not that one is in an N-state. One can believe one is in a pain state without believing that one is in an N-state because the concept of pain is different from the concept of N. Nevertheless, pain is N. (Compare the fact that while water is H2O, the concept of water is different from that of H2O. Thus, while water is H2O, one can believe there is water in the glass without believing that there is H2O in it. The avenue of privileged access presents N conceptualized as pain, but never as neurological state N. The avenue of privileged access involves the exercise of mental, but not neurophysiological, concepts. However, our mental concepts answer to – apply in virtue of – the same properties (state types) as do certain of our neurophysiological concepts. The identity theory and central state materialism both hold that there are contingent psychophysical property and type identities. Some theorists in this tradition tried to distinguish a notion of theoretical identity from the notion of strict identity. They held that mental states are theoretically, but not strictly, identical with brain states. Against any such distinction, Kripke argued that identities are metaphysically necessary, i.e., hold in every possible world. If A % B, then necessarily A % B. Kripke acknowledged that there can be contingent statements of identity. But such statements, he argued, will employ at least one term that is not a rigid designator, i.e., a term that designates the same thing in every world in which it designates anything. Thus, since ‘the inventor of bifocals’ is a non-rigid designator, ‘Benjamin Franklin is the inventor of bifocals’ is contingent. While Franklin is the inventor of bifocals, he might not have been. However, statements of identity in which the identity sign is flanked by rigid designators are, if true, metaphysically necessary. Kripke held that proper names are rigid designators, and hence, the true identity statement ‘Cicero is Tully’ is metaphysically necessary. Nonetheless, a metaphysically necessary identity statement can be knowable only a posteriori. Indeed, ‘Cicero is Tully’ is knowable only a posteriori. Both ‘water’ and ‘H2O’, he maintained, are rigid designators: each designates the same kind of stuff in every possible world. And he thus maintained that it is metaphysically necessary that water is H2O, despite its not being a priori knowable that water is H2O. On Kripke’s view, any psychophysical identity statement that employs mental terms and physical terms that are rigid designators will also be metaphysically necessary, if true.
Central state materialists maintain that mental concepts are equivalent to concepts whose descriptive content is the state that is apt to produce such-and-such behavior in such-and-such circumstances. These defining descriptions for mental concepts are intended to be meaning-giving, not contingent reference-fixing descriptions; they are, moreover, not rigid designators. Thus, the central state materialists can concede that all identities are necessary, but maintain that psychophysical claims of identity are contingent claims of identity since the mental terms that figure in those statements are not rigid designators. However, Kripke maintained that our concepts of sensations and other qualitative states are not equivalent to the sorts of descriptions in question. The term ‘pain’, he maintained, is a rigid designator. This position might be refuted by a successful functional analysis of the concept of pain in physical and/or topic-neutral terms. However, no successful analysis of this sort has yet been produced. (See the section on consciousness below.)
A materialist can grant Kripke that ‘pain’ is a rigid designator and claim that a statement such as ‘Pain is C-fiber firing’ will be metaphysically necessary if true, but only a posteriori knowable. However, Kripke raised a formidable problem for this materialism. He pointed out that if a statement is metaphysically necessary but only a posteriori knowable, its appearance of contingency calls for explanation. Despite being metaphysically necessary, ‘Water is H2O’ appears contingent. According to Kripke, we explain this appearance by noting that one can coherently imagine a world in which something has all the phenomenal properties of water, and so is an ‘epistemic counterpart’ of it, yet is not H2O. The fact that we can coherently imagine such epistemic counterparts explains why ‘Water is H2O’ appears contingent. But