he cognitive
faculty will always judge of its own impression as such; and so every
judgment will be true: for instance, if taste perceived only its own
impression, when anyone with a healthy taste perceives that honey is
sweet, he would judge truly; and if anyone with a corrupt taste
perceives that honey is bitter, this would be equally true; for each
would judge according to the impression on his taste. Thus every
opinion would be equally true; in fact, every sort of apprehension.

Therefore it must be said that the intelligible species is related to
the intellect as that by which it understands: which is proved thus.
There is a twofold action (Metaph. ix, Did. viii, 8), one which
remains in the agent; for instance, to see and to understand; and
another which passes into an external object; for instance, to heat
and to cut; and each of these actions proceeds in virtue of some
form. And as the form from which proceeds an act tending to something
external is the likeness of the object of the action, as heat in the
heater is a likeness of the thing heated; so the form from which
proceeds an action remaining in the agent is the likeness of the
object. Hence that by which the sight sees is the likeness of the
visible thing; and the likeness of the thing understood, that is, the
intelligible species, is the form by which the intellect understands.
But since the intellect reflects upon itself, by such reflection it
understands both its own act of intelligence, and the species by
which it understands. Thus the intelligible species is that which is
understood secondarily; but that which is primarily understood is the
object, of which the species is the likeness. This also appears from
the opinion of the ancient philosophers, who said that "like is known
by like." For they said that the soul knows the earth outside itself,
by the earth within itself; and so of the rest. If, therefore, we
take the species of the earth instead of the earth, according to
Aristotle (De Anima iii, 8), who says "that a stone is not in the
soul, but only the likeness of the stone"; it follows that the soul
knows external things by means of its intelligible species.

Reply Obj. 1: The thing understood is in the intellect by its own
likeness; and it is in this sense that we say that the thing actually
understood is the intellect in act, because the likeness of the thing
understood is the form of the intellect, as the likeness of a
sensible thing is the