 With this distinction we seem to have, at last, the classic division between the purely theoretical and the purely practical. Scientific knowledge concerns itself with the world of necessary truths, which stands apart from the world of everyday contingencies, the province of craft. Still, there are many problems of interpretation surrounding this description of scientific knowledge in Posterior Analytics. While we cannot address them in this article, we can at least point out a central one. The description just given of epistêmê makes scientific knowledge into a deductive system in which the relations among terms are invariable and necessary. The problem for commentators has been how to reconcile this description of epistêmê with Aristotle’s actual procedure in such treatises as the Physics and De Anima, where one does not find a deductive system of invariable and necessary relations. One possible explanation is that these treatises are preliminary sketches for a truly scientific treatise. So one could envision another Physics which would be a series of deductions, all expressing invariable and necessary truths about nature. However, this charitable assessment does not avoid all problems. In Metaphysics II, Aristotle explicitly undermines the possibility of an epistêmê, in the strict sense, with respect to nature. At the end of Book II, Aristotle makes a distinction between the accuracy to be found in mathematics and that in other disciplines. Mathematical accuracy, he says, cannot be expected in all things but only in those which do not contain matter. In particular, then, one cannot expect mathematical accuracy in the study of nature since it is concerned with matter (995a15–20). If ‘mathematical accuracy’ means the grasp of necessary and invariable relations among terms, then the study of nature will, by definition, have no such accuracy because what it studies contains matter. About nature, then, we might have to settle for something less than epistêmê in the strict sense. Indeed, in Book VI of the Metaphysics, Aristotle seems to make a major concession on the issue of epistêmê when he says that there is no knowledge of the accidental, i.e., what happens infrequently, because all epistêmê is of that which is always or for the most part (hôs epi to polu) (1027a20). Instead of grasping what is always and necessary, knowledge can then grasp what happens for the most part, e.g., the regularities of nature, to which there are exceptions.