Token Identity theories hold that every concrete particular falling under a mental kind can be identified with some physical (perhaps neurophysiological) happening or other: instances of pain, for example, are taken to be not only instances of a mental state (., pain), but instances of some physical state as well (say, c-fiber excitation). Token Identity is weaker than Type Identity, which goes so far as to claim that mental kinds themselves are physical kinds. As Jerry Fodor pointed out in 1974, Token Identity is entailed by, but does not entail, Type Identity. The former is entailed by the latter because if mental kinds themselves are physical kinds, then each individual instance of a mental kind will also be an individual instance of a physical kind. The former does not entail the latter, however, because even if a concrete particular falls under both a mental kind and a physical kind, this contingent fact "does not guarantee the identity of the kinds whose instantiation constitutes the concrete particulars."