 Mill’s descriptivism implies that for each natural kind term there is an associated set of properties such that for some item to be a member of that natural kind, it should possess those properties—these are properties that describe objects belonging to the kind in question. Implicit in Mill and explicit in Frege is the claim that these descriptions are constitutive of the meaning of the term in the following way: someone who understands the term adequately will be in a position to grasp a priori that something falls under the kind term if and only if it satisfies that description. For this reason the relevant properties will normally be readily observable properties of things; they will not be properties associated with the kind only by a posteriori investigation. For example, as mentioned above, Kant held the view that it is a priori that something falls under the kind term gold only if it is a yellow metal. Because the extension-fixing meaning of a term is thus graspable a priori this view is internalist about extension fixing. The extensions of kind terms of any two subjects with the same internal mental states will have (in the same context) the same extensions.