how a symbolic cognitive architecture is realized in the nervous system.
Content externalism. Many today hold that Twin-Earth thought experiments by Putnam and Tyler Burge show that the contents of a subject’s mental states do not supervene on intrinsic properties of the subject: two individuals can be exactly alike in every intrinsic respect, yet be in mental states with different contents. (In response to Twin-Earth thought experiments, some philosophers have, however, attempted to characterize a notion of narrow content, a kind of content that supervenes on intrinsic properties of thinkers.) Content, externalists claim, depends on extrinsic-contextual factors. If externalism is correct, then a psychosemantic theory must examine the relation between mental symbols and the extrinsic, contextual factors that determine contents. Stephen Stich has argued that psychology should eschew psychosemantics and concern itself only with the syntactic properties of mental sentences. Such a psychology could not explain intentional capacities. But Stich urges that computational psychology also eschew that explanatory goal. If, however, psychology is to explain intentional capacities, a psychosemantic theory is needed. Dretske, Fodor, Ruth Millikan, and David Papineau have each independently attempted to provide, in physicalistically respectable terms, foundations for a naturalized externalist theory of the content of mental sentences or internal physical states. Perhaps the leading problem for these theories of content is to explain how the physical and functional facts about a state determine a unique content for it. Appealing to work by Quine and by Kripke, some philosophers argue that such facts will not determine unique contents. Both causal and epistemic concerns have been raised about externalist theories of content. Such theories invite the question whether the property of having a certain content is ever causally relevant. If content is a contextual property of a state that has it, can states have effects in virtue of their having a certain content? This is an important issue because intentional states figure in explanations not only in virtue of their intentional mode (whether they are beliefs, or desires, etc.) but also in virtue of their contents. Consider an everyday belief-desire explanation. The fact that the subject’s belief was that there was milk in the refrigerator and the fact that the subject’s desire was for milk are both essential to the belief and desire explaining why the subject went to the refrigerator. Dretske, who maintains that content depends on a causal-historical context, has attempted to explain how the property of having a certain content can be causally relevant even though the possession of the property depends on causal-historical factors. And various other philosophers have attempted to explain how the causal relevance of content can be squared with the fact that it fails to supervene on intrinsic properties of the subject. A further controversial question is whether externalism is consistent with our having privileged access to what we are thinking. Consciousness. Conscious states such as pain states, visual experiences, and so on, are such that it is ‘like’ something for the subject of the state to be in them. Such states have a qualitative aspect, a phenomenological character. The what-it-is-like aspects of experiences are called qualia. Qualia pose a serious difficulty for physicalism. Broad argued that one can know all the physical properties of a chemical and how it causally interacts with other physical phenomena and yet not know what it is like to smell it. He concluded that the smell of the chemical is not itself a physical property, but rather an irreducible emergent property. Frank Jackson has recently defended a version of the argument, which has been dubbed the knowledge argument. Jackson argues that a super-scientist, Mary, who knows all the physical and functional facts about color vision, light, and matter, but has never experienced redness since she has spent her entire life in a black and white room, would not know what it is like to visually experience red. He concludes that the physical and functional (topic-neutral) facts do not entail all the facts, and thus materialism is false. In response, Lawrence Nemirow, David Lewis, and others have argued that knowing what it is like to be in a certain conscious state is, in part, a matter of know-how (e.g., to be able to imagine oneself in the state) rather than factual knowledge, and that the failure of knowledge of the physical and functional facts to yield such know-how does not imply the falsity of materialism.
Functionalism seems unable to solve the problem of qualia since qualia seem not to be functionally definable. In the 1970s, Fodor and Ned Block argued that two states can have the same causal role, thereby realizing the same functional state, yet the qualia associated with each can be inverted. This is called the problem of inverted qualia. The color spectrum, e.g., might be inverted for two individuals (a possibility raised by Locke), despite their being in the same functional states. They further argued that two states might realize the same functional state, yet the one might have qualia associated with it and the other not. This is called the problem of absent qualia. Sydney Shoemaker has argued that the possibility of absent qualia can be ruled out on functionalist grounds. However, he has also refined the inverted qualia scenario and further articulated the problem it poses for functionalism. Whether functionalism or physicalism can avoid the problems of absent and inverted qualia remains an open question.
Thomas Nagel claims that conscious states are subjective: to fully understand them, one must understand what it is like to be in them, but one can do that only by taking up the experiential point of view of a subject in them. Physical states, in contrast, are objective. Physical science attempts to characterize the world in abstraction from the experiential point of view of any subject. According to Nagel, whether phenomenal mental states reduce to physical states turns on whether subjective states reduce to objective states; and, at present, he claims, we have no understanding of how they could. Nagel has suggested that consciousness may be explainable only by appeal to as yet undiscovered basic nonmental, non-physical properties – ‘proto-mental properties’ – the idea being that experiential points of view might be constituted by protomental properties together with physical properties. He thus claims that panphysicism is worthy of serious consideration. Frank Jackson, James Van Cleve, and David Chalmers have argued that conscious properties are emergent, i.e., fundamental, irreducible macro-properties; and Chalmers sympathizes with a brand of panphysicism. Colin McGinn claims that while conscious properties are likely reductively explainable by brain properties, our minds seem conceptually closed to the explaining properties: we are unable to conceptualize them, just as a cat is unable to conceptualize a square root. Dennett attempts to explain consciousness in supervenient behaviorist terms. David Rosenthal argues that consciousness is a special case of intentionality – more specifically, that conscious states are just states we can come in a certain direct way to believe we are in. Dretske, William Lycan, and Michael Tye argue that conscious properties are intentional properties and physicalistically reducible. Patricia Churchland argues that conscious phenomena are reducible to neurological phenomena. Brian Loar contends that qualia are identical with either functional or neurological states of the brain; and Christopher Hill argues specifically that qualia are identical with neurological states. Loar and Hill attempt to explain away the appearance of contingency of psychophysical identity claims, but in a way different from the way Kripke attempts to explain the appearance of contingency of ‘Water is H2O’, since they concede that that mode of explanation is unavailable. They appeal to differences in the conceptual roles of neurological and functional concepts by contrast with phenomenal concepts. They argue that while such concepts are different, they answer to the same properties. The nature of consciousness thus remains a matter of dispute. See also ACTION THEORY, COGNITIVE SCI- ENCE , CONNECTIONISM , FOLK PSYCHOLOGY, INTENTIONALITY, MEANING , PHILOSOPHY OF LANGUAGE , PHILOSOPHY OF SCIENCE , PHYSI – CALIS. B.P.M.