Universal propositions are grasped through analogical inference.
One indication that certain knowledge—whether of universals or of particulars—does not depend on the logicians’ demonstrative method is this: their demonstration must contain a universal premise, yet knowledge of that universal premise itself demands a cause. If they acquire it by extrapolating the unseen from the seen—on the basis that the ruling applied to one thing applies equally to its counterpart—then they are reasoning by analogy. Thus, when we perceive that this fire burns and consequently conclude that a distant fire burns because it resembles the first, we are applying the principle that “the ruling of a thing extends to its like.” This, however, is precisely analogical inference, which they themselves admit yields only probability, not certainty. Hence, when they come to know a universal premise through analogy, their purported certainty ultimately rests on what they concede can provide no more than conjecture.
If they object that, upon sensing particulars, the soul receives knowledge of universals from the Bestower of intellect—or that the perception of particulars merely disposes the soul so that universals overflow into it from that Bestower, or, in their terminology, from the Active Intellect, and the like—our response is: the issue is how one knows that the universal judgment present in the soul is knowledge, not conjecture or ignorance.
Should they reply that this is grasped intuitively and by necessity, they have conceded that these universal propositions are known by intuition and necessity and that the soul is compelled to them. If this is so, then knowledge of concrete particulars and of the various classes of universals likewise arises in the soul intuitively and necessarily, as experience confirms.
Indeed, the certainty possessed by rational people regarding individual sensibles is stronger than their certainty regarding universals, and their conviction about the universality of species surpasses their conviction about the universality of genera, while knowledge of particulars