 Many philosophers identify themselves as functionalists (see  functionalism)  about mental states in general or belief in particular. Functionalism about mental states is the view that what makes something a mental state of a particular type are its actual and potential, or its typical, causal relations to sensory stimulations, behavior, and other mental states (seminal sources include Armstrong 1968; Fodor 1968; Lewis 1972, 1980; Putnam 1975; Block 1978). Functionalists generally contrast their view with the view that what makes something a mental state of a particular type are facts about its internal structure. To understand this distinction, it may be helpful to begin with some non-mental examples. Arguably, what makes something a streptococcal bacterium, or a cube, is its shape or internal structure; its causal history or proneness to produce particular effects on particular occasions is only secondarily relevant, if at all. In contrast, whether something is a hard drive or not is not principally a matter of internal structure. A hard drive could be made of plastic or steel, employ magnetic tape or lasers. What matters are the causal relationships it’s prone to enter with a computer: Under certain promptings, it enters states such that, under certain further promptings, it will generate outputs of a certain sort. Internal structure is relevant only secondarily, insofar as it grounds these causal capacities. Likewise, according to the functionalist, what makes a state pain is not its particular neural configuration. People and animals with very different neural configurations could all equally be in pain (even, conceivably, a Martian with an internal structure radically different from ours could suffer pain). What matters is that the subject is in a state that (roughly) is apt to be caused by tissue damage or tissue stress and that, in turn, is apt to cause signs of distress, withdrawal, future avoidance of the painful stimulus, and (in verbal subjects) thoughts and utterances like “that hurts!”.