What is the best way to understand 'applies to' when it is said of a linguistic theory that it applies to a particular language-user? We can answer by saying that a linguistic theory is applicable to an individual language-user just in case that individual tacitly-knows the theory. But this is an uninformative answer until we are told how to understand 'tacit-knowledge'. The end goal of this thesis is to defend the claim that we should take tacit-knowledge to be, simply, knowledge. (...) Towards this end I argue against the satisfactoriness of competing ways of understanding 'tacit-knowledge'. For example, the instrumentalist position is neutral on whether linguistic theories are actually known by the ordinary language-users who tacitly-know them; instead, linguistic theories are to be such that knowing them would enable someone to do whatever it is that the tacit-knower can do. Other competing positions hold that, though tacit-knowledge is a psychological relation of some sort, it is not genuine knowledge. I also attempt to meet specific objections to the claim that a typical language-user could plausibly be said to know a linguistic theory. An objection on which I focus is based on the claim that typical language-users do not possess the requisite concepts for having genuine knowledge of a linguistic theory. The aim in attempting to meet these objections is to open up the way for the linguistic theorist to exploit a paradigm of explanation: explanation of behaviour by knowledge attribution. Attributing knowledge of linguistic theories would be potentially explanatory of linguistic behaviour in exactly the same way that attributions of knowledge in non-linguistic spheres are potentially explanatory of behaviour. Finally, because my emphasis is specifically on semantic theories, I attempt to explicate and defend the claim that a semantic theory could and should have the form of a theory of truth. (shrink)