as a necessary concomitant of the categories, and with similarity, difference, opposition, and otherness as necessary concomitants of numerous distinct realities. For although blackness and whiteness differ, they share the fact that each is the opposite of the other.

As for the second case—where that in which things differ is a necessary concomitant of what they share—this is impossible. Consider rationality in relation to animality: if rationality necessarily followed from animality, every animal would be rational.

As for the third and fourth cases, both are possible.”

I say:

This argument rests on principles conceded to them by those who did not understand them, such as their distinction between essential constitutive attributes and necessary accidental attributes, their claim that species are composed of genera and differentiae, and similar matters.

We shall explain how the truth may be known.

We say:

It is evident that this human being resembles others in humanity and resembles all other animals in animality. This is what they mean when they say that two individuals agree in what is designated by humanity or animality, or that they share in it. Yet no one else shares in the very humanity particular to him, or in the animality particular to him, even though others are like him and resemble him in these respects. One thing’s resemblance or likeness to another does not entail that the other shares in its very entity or in any of the attributes inhering in it. Thus, the particular individual Zayd has nothing of anyone else in him, nor in any of the attributes inhering in him.

Hence, statements such as “They share in humanity” or “They agree in it” are ambiguous, for sharing may mean sharing in things existing in external reality,