 Why was Quine so convinced of this last claim? Because he thought it was possible to provide a satisfactory explanation of human language without them, indeed, without any mentalistic notions at all. In his (1953 [1980b], 1960 [2013] and 1974) he sketched a behavioristic theory of language that doesn’t rely on the postulation of determinate meaning or reference, and argued that, indeed, translation is “indeterminate”: there is “no fact of the matter” about whether two expressions do or do not have the same meaning (see Indeterminacy of Translation). This would appear to imply that there are pretty much no facts of the matter about people’s mental lives at all! For, if there is no fact of the matter about whether two people mean the same thing by their words, then there is no fact of the matter about the content of anyone’s thoughts. Quine himself took this consequence in stride—he was, after all, a behaviorist– regarding it as “of a piece” with Franz Brentano’s (1874 [1995]) famous thesis of the “irreducibility of the intentional”; it’s just that for him, unlike for Brentano, it simply showed the “baselessness of intentional idioms and the emptiness of a science of intention” (1960 [2013], p. 202). Needless to say, many subsequent philosophers have not been happy with this view, and have wondered where Quine’s argument went wrong.