—entails an absolute quiddity shared by the two, and from this it does not follow that the nature must be accompanied by different concomitants. On the contrary, a single, universal, absolute, common nature is attended by one single, common, universal attribute. If, however, you take the necessary existence proper to each one of them—namely, the determinate necessary existence that is realized in external reality—then what corresponds to it is a determinate quiddity likewise established externally.

Moreover, when someone speaks of “the single nature,” he may mean what is numerically one or what is one in species; this, as we have already shown in answering the preliminary premise of the question, is the root of their misguidance in this matter. Thus the expression “the single nature,” like the expressions “the essence,” “the one existence,” “the one human being,” and the like, may indicate either unity of species or unity of individual.

The philosophers say that unity falls into eight divisions: (1) the truly real one, (2) the one by continuity, (3) the one by conjunction, (4) the one in genus, (5) the one in species, (6) the accidental one, (7) the relative one, and (8) the one in subject.

Yet all of these revert to the two divisions we have already mentioned. They say: The truly real one is that which admits no multiplicity whatsoever, neither actually nor potentially, such as a single point that is absolutely indivisible (1)—whether in actuality, in imagination, or even by mental supposition—or such as the essence of Allah Most High or the essence of the Intellect. It has been demonstrated elsewhere that this “one” they describe has no reality outside the mind; it can exist only as a mental conception.

The one by continuity is that which has no actual multiplicity but does contain multiplicity in potentiality, such as a single line, a single surface, or a single homogeneous body, for the continuity that obtains (2)—