John Buridan was a remarkable and courageous man. Remarkably consistent. He almost invariably says the same about the same things, and what he say about one subject is usually consistent with what he says about any other somehow related subject. His works abound in cross-references, from one part of a work to another, and from one work to another. He obviously wanted his readers to think of his philosophical works as one coherent corpus presenting one coherent philosophy. Perhaps this ought to scare the historian away from an attempt to interpret Buridan on the basis of one work. But, on the other hand, the fact that he very rarely disagrees with himself and the fact that he repeats his basic tenets in every work make it possible to reconstruct the essentials of Buridanian philosophy without using all available sources, in particular because his pen was as sharp as his mind. His prose possesses to an eminent degree the virtue of clarity. This paper is based on treatise 8 of his Summulae, or Handbook of Logic. As subsidiary sources I have used the remaining part of the Summulae and his quaestiones on the Prior and Posterior Analytics and on the Metaphysics. 2