Mind: A Brief Introduction (John R. Searle) / quote 123 of 138
Intentionality-with-a-t and intensionality-with-an-s
Intentionality-with-a-t, as we have seen, is that property of the mind by which it is directed at or about or of objects and states of affairs in the world independent of itself. Intensionality-with-an-s is opposed to extensionality. It is a property of certain sentences, statements, and other linguistic entities by which they fail to meet certain tests for extensionality. The connection between the two is that many sentences about intentional-with-a-t states are intensional-with-an-s sentences. There are several such tests for extensionality, but the two most famous are the substitution test (sometimes called Leibnitz’s Law) and the test of existential inference. Let us consider each of these in order. The substitution test…