 According to the philosophical tradition, to know the meaning of a subsentential expression like ‘bachelor’ is to implicitly grasp a criterion that determines exactly which individuals count as bachelors in any possible situation. (Accounts of meaning broadly along these lines were advanced by Plato, Descartes, Locke, Hume, Frege, Russell, Carnap, and many others.) On the traditional account, speakers’ implicit grasp of a criterion plays two key theoretical roles: