His statement: “The second alternative is to say that these parts differ in essence. We say: Every body composed of parts differing in essence must ultimately, upon analysis of its composition, resolve into parts each of which is free of such composition, for composition means the joining together of units.”

It may be replied: Grant that its composition resolves into parts each of which is free of such composition. Yet this does not require those parts to be alike in quality and reality, even if they are indivisible atoms. Rather, one may say that they are equal in magnitude, in the sense that they cannot be divided, without being alike in quality and reality. Indeed, the reality of each of those parts differs from that of the others. This means that indivisible atoms are equal in magnitude but unequal in reality. This is the view of many people, or most of them.

Indeed, most people in the world hold that substances are not alike in reality. Although they disagree as to whether substance constitutes one genus, two genera, three, or more, they generally agree that the members of a single genus are not all alike; rather, it comprises different species. Thus, if those who hold that they constitute a single genus