 Here are a few well-known arguments by appeal to a FIST. Suppose someone claims that there are neurophysiological properties, perhaps yet to be discovered, to which intentional properties like believing that P reduce. This claim implies that intentional properties supervene on neurophysiological properties. The Twin Earth thought experiments given by Tyler Burge (1979) and Hilary Putnam (1976) are (putative) counterexamples to that supervenience claim; they are cases of neurophysiologically indiscernible people whose thoughts have different contents.