are
mixed up with the mind. Hence the purer the intellect is, so much the
more clearly does it perceive the intelligible truth of immaterial
things.

But in Aristotle's opinion, which experience corroborates, our
intellect in its present state of life has a natural relationship to
the natures of material things; and therefore it can only understand
by turning to the phantasms, as we have said above (Q. 84, A. 7).
Thus it clearly appears that immaterial substances which do not fall
under sense and imagination, cannot first and _per se_ be known by us,
according to the mode of knowledge which experience proves us to have.

Nevertheless Averroes (Comment. De Anima iii) teaches that in this
present life man can in the end arrive at the knowledge of separate
substances by being coupled or united to some separate substance,
which he calls the "active intellect," and which, being a separate
substance itself, can naturally understand separate substances. Hence,
when it is perfectly united to us so that by its means we are able to
understand perfectly, we also shall be able to understand separate
substances, as in the present life through the medium of the passive
intellect united to us, we can understand material things. Now he
said that the active intellect is united to us, thus. For since we
understand by means of both the active intellect and intelligible
objects, as, for instance, we understand conclusions by principles
understood; it is clear that the active intellect must be compared to
the objects understood, either as the principal agent is to the
instrument, or as form to matter. For an action is ascribed to two
principles in one of these two ways; to a principal agent and to an
instrument, as cutting to the workman and the saw; to a form and its
subject, as heating to heat and fire. In both these ways the active
intellect can be compared to the intelligible object as perfection is
to the perfectible, and as act is to potentiality. Now a subject is
made perfect and receives its perfection at one and the same time, as
the reception of what is actually visible synchronizes with the
reception of light in the eye. Therefore the passive intellect
receives the intelligible object and the active intellect together;
and the more numerous the intelligible objects received, so much the
nearer do we come to the point of perfect union between ourselves and
the active intellect; so much so that when we understand all the
intell