that would have to be added to the genus "being" to form the species "True" and "possible" would therefore have to add something to th genus "being" that, up to that point, it itself is not. Yet surely the true and the possible are not nothing at all but something: otherwise the genus "being" would be unable to determine them. But if they are something, n. then they are the kind of things to which being belongs. Hence, the species-forming differentiae are beings of some sort in the broadest sense, that is, something that is determined by being. Therefore, being, which is attributable to anything that is not nothing. and indeed even to this, already expresses the species-forming differentiae, the true and the possible, as something that is. But for a genus to be able to be a genus, it may include nothing of the content of the species-forming differentiae. Since being, as what is able to be said most universally, must include this, it cannot have the character of a unity for the many in the manner of a genus; and the various ways of being cannot be understood as species.
Βeing cannot be a genus, cannot be said συνωνύμως. We can further extend our reflections on this proposition of Aristotle's. The universal, comprehended and defined as species-enabling genus, is usually called "concept." If being is not a genus, then it cannot be comprehended as a concept, nor can it be conceptualized. This is so not just because there is no higher genus than the genus of being, but also because being is not a genus at all. If the delimitation of a concept ὁρισμός is called definition, then this means that all definitional determinations of being must on principle fail. If being is to be comprehended at all, then it must be in a completely different way. We will find this explicated in the treatise on δύναμις and ἐνέργεια.
The proof of the non-genus-like character of being tells us only which characteristics the oneness of being is not. Had Aristotle done nothing but work out this negative answer, it would be proof enough that the question of the oneness of being was a real question for him. Since for both the earlier and the later Plato all determinations of being and being itself remained γένος, the Aristotelian statement of the problem announces a fundamental rejection of the Platonic conception of being-and a decisive step closer to the essence of being. (Whether the cited indirect proof is itself intrinsically valid will not be discussed here.)