Among the commentaries on Aristotle's Physics produced by medieval masters in the 14th Century Oresme's is one of the most interesting. The main problems of natural philosophy (motion, time, intension and remission of forms) as well as cognitive and ontological issues are widely discussed. Oresme proposes original solutions to most of these topics, based on an original view concerning the relationship between substance and its properties (condicio/condiciones, modi rerum); Oresme’s solutions are always associated with sharp criticism of the two main philosophical schools: the realists (Walter Burley) and the nominalist (William Ockham). This commentary is a very valuable record of the philosophical discussions at Paris in the midst of the 14th Century.