Some recent studies show in John Buridan a noteworthy degree of originality and innovation in his treatment of Aristotle’s theory of science, for example concerning the doctrines of subalternation of the sciences, or some aspects of the doctrine of definition, which are between the main themes of Posterior Analytics. In this paper, two other topics are investigated: first, the interpretation of the fourth mode of per se predication, about which Buridan in the Summulae proposes a new, original and interesting view definitely overcoming either the previous exegetical tradition, or the opinion Buridan himself expresses in his Questiones on Aristotle’s text. The second is the topic of propter quid demonstration, that Buridan deepens also in order to go beyond the old and maybe almost outdated quaestio de medio demonstrationis. But, what is more, he is higly consistent and very original in connecting these two topics: so, he gives a new unity and systematic order also to some other minor aspect of his reading of Aristotelian theory.
Keywords: John Buridan, demonstration, per se predication, Aristotelian tradition, theory of science.