 There is yet another distinction between kinds of functional theory — one that crosscuts the distinctions described so far — that is important to note. This is the distinction between what has come to be known as “role” functionalism and “realizer” (or “filler”) functionalism (McLaughlin 2006). To see the difference between these types of theory, consider—once again—the (avowedly simplistic) example of a functional theory of pain introduced in the first section.