ed "passive"--Ed.]. Therefore in its essence the
human mind is potentially understanding. Hence it has in itself the
power to understand, but not to be understood, except as it is made
actual. For even the Platonists asserted that an order of
intelligible beings existed above the order of intellects, forasmuch
as the intellect understands only by participation of the
intelligible; for they said that the participator is below what it
participates. If, therefore, the human intellect, as the Platonists
held, became actual by participating separate intelligible forms, it
would understand itself by such participation of incorporeal beings.
But as in this life our intellect has material and sensible things
for its proper natural object, as stated above (Q. 84, A. 7), it
understands itself according as it is made actual by the species
abstracted from sensible things, through the light of the active
intellect, which not only actuates the intelligible things
themselves, but also, by their instrumentality, actuates the passive
intellect. Therefore the intellect knows itself not by its essence,
but by its act. This happens in two ways: In the first place,
singularly, as when Socrates or Plato perceives that he has an
intellectual soul because he perceives that he understands. In the
second place, universally, as when we consider the nature of the
human mind from knowledge of the intellectual act. It is true,
however, that the judgment and force of this knowledge, whereby we
know the nature of the soul, comes to us according to the derivation
of our intellectual light from the Divine Truth which contains the
types of all things as above stated (Q. 84, A. 5). Hence Augustine
says (De Trin. ix, 6): "We gaze on the inviolable truth whence we can
as perfectly as possible define, not what each man's mind is, but
what it ought to be in the light of the eternal types." There is,
however, a difference between these two kinds of knowledge, and it
consists in this, that the mere presence of the mind suffices for the
first; the mind itself being the principle of action whereby it
perceives itself, and hence it is said to know itself by its own
presence. But as regards the second kind of knowledge, the mere
presence of the mind does not suffice, and there is further required
a careful and subtle inquiry. Hence many are ignorant of the soul's
nature, and many have erred about it. So Augustine says (De Trin. x,
9), concerning such mental inquiry