The attempt to separate what is essential from what is an inseparable accident is even more far-fetched. For that reason Ibn Sīnā nullified the distinction, as we have quoted his own words elsewhere: on either reading there remain concomitants that are affirmed without any middle term.

Accordingly, if one defines the essential as “that which is affirmed without a middle term,” while conceding that certain concomitants are likewise affirmed without a middle term, the failure of this distinction becomes manifest in every respect.

Variation in people’s need for proof
It is likewise clear that the middle term—that is, the evidence—may be needed by some people in certain propositions but not by others. A given proposition may strike one person as perceptual, experimental, demonstrative, or mass-transmitted, yet reach another only through reflection and inference.

Hence many people require no proof for themselves that the predicate belongs to the subject; they supply proofs only for the sake of others. They put forward arguments they themselves can dispense with, offering examples and asking, “Is it not so? Is it not so?” They adduce rational and scriptural evidences that function as a middle term for the addressee, though not for the speaker. A person may know a thing directly through sense perception and still marshal evidence to establish it for someone else.

This is too obvious to need illustration. How many observers see the stars or sight the crescent moon and declare, “The new moon has appeared!”—a proposition that for them is sensory fact—while for others it remains doubtful, conjectural, or merely report-based. Indeed, a listener might even deem it false if he has trusted a mendacious astrologer who insists the moon is not visible.