  After Ryle, philosophers sought a more explicit and generally naturalistic ontology of mind. In the 1950s materialism was argued anew, urging that mental states are identical with states of the central nervous system. The classical identity theory holds that each token mental state (in a particular person’s mind at a particular time) is identical with a token brain state (in that person’s brain at that time). A stronger materialism holds, instead, that each type of mental state is identical with a type of brain state. But materialism does not fit comfortably with phenomenology. For it is not obvious how conscious mental states as we experience them—sensations, thoughts, emotions—can simply be the complex neural states that somehow subserve or implement them. If mental states and neural states are simply identical, in token or in type, where in our scientific theory of mind does the phenomenology occur—is it not simply replaced by neuroscience? And yet experience is part of what is to be explained by neuroscience.