 Chomsky’s project is to work towards a scientifically credible understanding of a natural object, the human brain. More feasibly, his ambition is to make progress on understanding those aspects of the brain that are central to our nature as linguistic beings. A reasonable starting hypothesis for such an inquiry is that a functionally discrete part of the brain, the “language faculty”, is responsible for core elements of our capacity to use language. If this hypothesis is right, other parts of the brain, and plenty that lies outside the brain in our external social and physical environment, may well combine with this language faculty to produce linguistic behaviour; but the inquiry itself is limited to understanding the language faculty itself. This voluntary limitation has a rationale. Our overt behaviour is extraordinarily complex, an intractable interaction effect, so we need to be appropriately modest in our explanatory ambitions. A scientific understanding of the internal workings of the language faculty would in itself be a massive achievement. Linguistic behaviour—the sounds language-users produce, their description of certain constructions as ungrammatical, etc.—can supply defeasible evidence for or against hypotheses we make about the language faculty proper, but we should not treat the description of overt behaviour as the goal of study. (In an earlier incarnation of much the same point, Chomsky distinguished between core competence and the use of that competence manifest in overt performance, arguing that competence is far more promising an object of linguistic inquiry than the latter. He moved away from this terminology after it gave rise to persistent misinterpretations. Competence, for example, has unintended normative connotations—we speak of people as having “poor competence in Spanish”.)