 Take, for example, Lefèvre’s discussion of the intension and remission of qualities in his Introductory Dialogue on Difficult Physics. This question is interesting because, despite Aristotle’s meager account (Physics V.22.26b1–8), it became a foundational question in medieval natural philosophy. Moreover, by the fourteenth century, the calculatores of Oxford and Parisian natural philosophers such as Nicole Oresme used mathematics to clarify their thinking on the topic. The notion of remission and intension is meant to explain how qualities change gradually, as we experience them to do. In order to resolve the problem, it was necessary to ask several questions. Are such qualities forms? Can different qualities or forms mix together in the same subject? Does change involve a series of new forms (the succession theory), or instead is it a changing mixture of qualities, so that a gray object is a mix of white and dark contraries (admixture theory)? Or do qualities gradually change as infinitesimal parts are gained or lost (addition theory)? (For the range of positions, see Kirschner 2000 and Di Liscia 2010.) In the Difficult Physics, Lefèvre’s view seems to be that qualities are not forms, since he never calls them anything other than qualities (a view similar to that of Buridan and Oresme; see Kirschner 2000). Moreover, he seems to adopt a version of an addition theory: a quality is intensified by adding another part or degree of that quality. Finally, he argues that contraries can be in the same subject only in a limited way—a certain amount of one quality would drive out (expellere) an excess of the other. Given a scale of heat from minimum to maximum, say from 1 to 10, one could also imagine a similar scale for cold from 10 to 1. Maximal cold could not coincide with maximal heat; but a low heat of 1 would coincide with a strong cold of 9. Increasing the heat to 4 would expel the cold, reducing it to 6.