Synthetic a priori proposition, in logic, a proposition the predicate of which is not logically or analytically contained in the subject—i.e., synthetic—and the truth of which is verifiable independently of experience—i.e., a priori. Thus the proposition “Some bodies are heavy” is synthetic because the idea of heaviness is not necessarily contained in that of bodies. On the other hand, the proposition “All husbands are male” is analytic because the idea of maleness is already contained in that of husband. In general the truth or falsity of synthetic statements is proved only by whether or not they conform to the way the world is and not by virtue of the meaning of the words they contain. Synthetic a priori knowledge is central to the thought of Immanuel Kant, who argued that some such a priori concepts are presupposed by the very possibility of experience.