The third distinction, they say, is that the proprium belongs to the quiddity through an intermediary, whereas the necessary accident belongs to it by means of a middle term. According to their foremost authorities—such as Ibn Sīnā—this “middle” is what they call the necessitating cause in that context; for some of their later writers, like al-Rāzī, it simply means the proof.

Yet they have contradicted themselves on this very point, as I have shown at length elsewhere when I quoted their own words and exposed their inconsistencies—citing, for example, Ibn Sīnā’s remarks in the Ishārāt and similar passages in their books. I am not reproducing their exact phrases here; my aim is only to draw attention to a set of general considerations by which the falsity of many of their logical claims becomes plain.

All that they have said rests on two unsound pillars: first, the purported distinction between quiddity and existence; and second, the purported distinction between what is essential to the quiddity and what merely accompanies it.

On the difference between quiddity and existence

The first pillar is their assertion that a quiddity possesses a reality in the external world distinct from its existence. This amounts to claiming that the absolute natures of species—the quiddities of species, genera, and all other universals—exist in concrete things. In one respect, it resembles the view of those who maintain that the nonexistent is nevertheless something. I have examined this in detail elsewhere, and it is among the most untenable of doctrines.

The root of their error is that they observed a thing to be known, desired, and distinguished—so that one can tell what lies within power and what lies beyond it—before the thing actually exists. They then concluded: if it were not somehow fixed in reality, none of this would be possible. Likewise, when we speak about the realities of things—that is, their quiddities—while abstracting from their external existence, we fall into the mistaken notion that these realities are entities established outside the mind.

The truth, however, is that all of this exists and is established only in the mind, not outside it. What the mind conceives can indeed be broader than what is found in concrete reality. It is present and fixed in the mind, but in fact it is neither existent nor fixed in external reality. Thus the very attempt to separate existence