From Descartes to Churchland

One of the clearest and most forceful denials of animal consciousness is developed by Rene Descartes (1596-1650), who argues that animals are automata that might act as if they are conscious, but really are not so (Regan and Singer, 1989: 13-19). Writing during the time when a mechanistic view of the natural world was replacing the Aristotelian conception, Descartes believed that all of animal behavior could be explained in purely mechanistic terms, and that no reference to conscious episodes was required for such an explanation. Relying on the principle of parsimony in scientific explanation (commonly referred to as Occam's Razor) Descartes preferred to explain animal behavior by relying on the simplest possible explanation of their behavior. Since it is possible to explain animal behavior without reference to inner episodes of awareness, doing so is simpler than relying on the assumption that animals are conscious, and is therefore the preferred explanation.

Descartes anticipates the response that his reasoning, if applicable to animal behavior, should apply equally well to human behavior. The mechanistic explanation of behavior does not apply to human beings, according to Descartes, for two reasons. First, human beings are capable of complex and novel behavior. This behavior is not the result of simple responses to stimuli, but is instead the result of our reasoning about the world as we perceive it. Second, human beings are capable of the kind of speech that expresses thoughts. Descartes was aware that some animals make sounds that might be thought to constitute speech, such as a parrot's "request" for food, but argued that these utterances are mere mechanically induced behaviors. Only human beings can engage in the kind of speech that is spontaneous and expresses thoughts.

Descartes' position on these matters was largely influenced by his philosophy of mind and ontology. According to Descartes, there are two mutually exclusive and jointly exhaustive kinds of entities or properties: material or physical entities on the one hand, and mental entities on the other. Although all people are closely associated with physical bodies, they are not identical with their bodies. Rather, they are identical with their souls, or the immaterial, mental substance that constitutes their consciousness. Descartes believed that both the complexity of human behavior and human speech requires the positing of such an immaterial substance in order to be explained. However, animal behavior does not require this kind of assumption; besides, Descartes argued, "it is more probable that worms and flies and caterpillars move mechanically than that they all have immortal souls" (Regan and Singer, 1989: 18).

http://www.iep.utm.edu/a/anim-eth.htm

Modern versions of eliminative materialism claim that our common-sense understanding of psychological states and processes is deeply mistaken and that some or all of our ordinary notions of mental states will have no home, at any level of analysis, in a sophisticated and accurate account of the mind. In other words, it is the view that certain common-sense mental states, such as beliefs and desires, do not exist.

Eliminative materialists argue that the central tenets of folk psychology radically misdescribe cognitive processes; consequently, the posits of folk psychology pick out nothing that is real. Like dualists, eliminative materialists insist that ordinary mental states can not in any way be reduced to or identified with neurological events or processes. However, unlike dualists, eliminativists claim there is nothing more to the mind than what occurs in the brain. The reason mental states are irreducible is not because they are non-physical; rather, it is because mental states, as described by common-sense psychology, do not really exist.

Some writers have suggested an eliminativist outlook not just with regard to particular states of consciousness, but with regard to phenomenal consciousness itself. For example, Georges Rey (1983, 1988) has argued that if we look at the various neurological or cognitive theories of what consciousness might amount to, such as internal monitoring or the possession of second-order representational states, it seems easy to imagine all of these features incorporated in a computational device that lacks anything we intuitively think of as "real" or robust consciousness. Rey suggests that the failure of these accounts to capture our ordinary notion of consciousness may be because the latter corresponds with no actual process or phenomenon; the "inner light" we associate with consciousness may be nothing more than a remnant of misguided Cartesian intuitions (see also Wilkes, 1988; 1995).

http://plato.stanford.edu/entries/materialism-eliminative/