Conventionalism is a doctrine about truth, typically mathematical truth. It says that when a proposition is true, the definitions of its terms make it so, and that the definitions hold when, as a rule, users of the relevant language understand by the definiendum just what they understand by the definiens, and apply the two interchangeably. Hobbes often writes as if he were a conventionalist with respect to the truth of all of the propositions of science.1 In The Elements of Law, for example, he contrasts experience-knowledge with science. Experience, he says, is the source of only one kind of knowledge. The other kind

is the remembrance of the names or appellations of things, and how every thing is called, which is, in matters of common conversation, a remembrance of pacts and covenants of men made amongst themselves, concerning how to be understood of one another. And this kind of knowledge is generally called science, and the conclusions thereof truth (Pt. 2, ch. 8, xii. 176).