 In the first lines of the eighth chapter of the Categories (8a25–26) Aristotle observes that quality is among those things that are spoken of in a number of ways—an affirmation which seems to imply that quality is not a highest genus, as, according to Aristotle himself, what is spoken of in a number of ways always gathers in several different natures. Furthermore, the Stagirite speaks of four species of quality (habits and dispositions, natural capacities and incapacities, affective qualities and affections, figures and shapes), without explaining how they are related to one another and to the highest genus of the category. No Aristotelian commentator had ever thought that quality was spoken of in many ways purely equivocally. Therefore no Aristotelian commentator had ever presumed that the term ‘quality’ could have several different (but connected) meanings. On the contrary, they unanimously took for granted that it had a unique ratio, common to all the items belonging to the category. They disagreed, however, about the status and hierarchical order of the four species mentioned by Aristotle. For example, Albert the Great held that quality at once and directly splits up into the four species, which would all be equally far from the highest genus. Duns Scotus, Ockham, and Walter Burley maintained that the so called ‘species’ of the quality were not properly species (or intermediate genera), but modes of quality, since many singular qualities would belong to the first three species at the same time, as, unlike species, modes are not constituted by opposite properties. Alyngton rejected both opinions. The latter because it compromises the actual goal of a correct categorial theory, and the former because it does not fit in with the standard infracatagorial structure described by Porphyry in his Isagoge. Consequently, he inserts an intermediate level between the highest genus of the category and the four species by claiming that quality is first of all divided into perceptible (sensibilis) and non-perceptible (insensibilis) qualities. Affective qualities and affections, figures and shapes stem from the former kind of quality, while habits and dispositions, natural capacities and incapacities derive from the latter. In fact, (1) figures and shapes are those perceptible qualities which inhere in substances because of the mutual position of its quantitative parts, while affective qualities and affections inhere in substances because of the form itself of the substantial composite. (2) Natural capacities and incapacities are inborn non-perceptible qualities, while habits and dispositions are due to the activity, both physical and, if it is the case, intellectual, of the substance in which they inhere (In Cat., cap. de qualitate, fol. 130r).