40. Being and the Ten Categories. -- Individual things alone having reality (43); the being which metaphysics studies by seizing on its general determinations, is simply the substance of the individual things (tode ti) presented to us in our sense-experience. There is in every being a primordial, constitutive element or basis, able to subsist by itself and which serves as a subject of inherence for all adventitious realities. Hence the first classification of beings into two categories, substance (ousia) and accident (sumbebêkos). Socrates is a substance; his virtue is an accident. The accident is next divided into nine categories; quality, quantity, relation, place, time, posture (keisthai), habit (echein) which is the possession resulting from change, action and passion implied in change (poiein kai paschein).^{1}

But to understand fully the scope of peripatetic metaphysics we must set this division, which is a statical one, over against another, which is a dynamic classification based on the change or flux of being: for the being which we know best and most fully is subject to change. Besides, each of the ten categories of being can be considered as in a state of change; it may be actual or potential.

{1} PIAT, op. cit., pp. 15 and 16. Historians are not agreed upon the sense of the last Categories, nor as to whether the nine accidents were reduced by Aristotle to one category, "accident".