ABSTRACT
THE idea that knowledge forms an ordered, hierarchical system is not a new one, but it has been particularly prominent in British philosophy in the last fifty years. It was anticipated by the theory of self-evidence put forward by Aristotle in the Posterior Analytics and assumed by Descartes in his pursuit of an indubitable startingpoint for the reconstruction of his beliefs. But where Aristotle and Descartes took the ultimate truths on which the edifice of knowledge was reared to be a priori principles, the more recent adherents of this general position have understood them to be particular statements of empirical fact.
