Thus a given piece of knowledge may simply dawn upon one person and settle in his mind as something self-evident, whereas another will reach it only after a short or lengthy process of deliberation—and indeed a third may find it hard to reach even through deliberation at all. We have already pointed this out when speaking of conceptions, yet here we shall add evidence specific to assent-propositions and say:
A judgement is self-evident when the mere conception of its two terms — its subject and predicate — is sufficient for assenting to it. It does not depend on any middle term between them, that is, on the proof that constitutes the “middle term,” whether or not the conception of those two terms itself is self-evident.
It is well known that people differ in mental aptitude far more than they do in physical strength. Some are possessed of such speed and sharpness of apprehension that they stand markedly apart from others; they form a complete conception of the two terms, and by virtue of that full conception the necessary concomitants become apparent—concomitants that remain hidden from someone who has not conceived the two terms so completely.
There are also those who conceive the two terms only through a handful of their distinguishing attributes. Yet the one who conceives them along with some of their shared attributes—whether these be called “essential” or something else—thereby knows that those attributes belong to the two terms, and likewise knows many of the properties that necessarily follow from them, unlike the person who grasped only the distinguishing attributes.
Invalidity of the distinction between the essential and the necessary concomitant, for each is established without a middle term.
The logicians themselves state that certain concomitants attach to their subjects without any middle term; such matters are known merely by conceiving the subject that entails them.
Moreover, the “middle” referred to in these discussions, according to Ibn Sīnā and the exacting thinkers who follow him, is none other than the proof itself.