The traditional doctrine of intension and extension, enshrined in nearly every elementary logic text (under the heading "Definitions"), is a litany of comfortable words. The extension of a (singular or general) term is, we are told, the class of things "it applies to", and its intension is that associated feature of the term in virtue of which it so applies—roughly, an assemblage of non-question-begging necessary conditions which are jointly sufficient for the term"s application. For most purposes, it is said, talk about the "meaning" of a term may be construed as talk about its intension: in particular, "knowing the meaning of a term" may be construed as knowledge of its intension, i.e., having a "mental representation" of the necessary-and-sufficient condition for its application. This beguilingly simple picture has undergone much technical refinement in the hands of logicians, whose formal implementations have contributed to its long and unbroken reign among semantic theorists.