igible objects, the active intellect becomes one with us, and
by its instrumentality we can understand all things material and
immaterial. In this he makes the ultimate happiness of man to consist.
Nor, as regards the present inquiry, does it matter whether the
passive intellect in that state of happiness understands separate
substances by the instrumentality of the active intellect, as he
himself maintains, or whether (as he says Alexander holds) the passive
intellect can never understand separate substances (because according
to him it is corruptible), but man understands separate substances by
means of the active intellect.

This opinion, however, is untrue. First, because, supposing the active
intellect to be a separate substance, we could not formally understand
by its instrumentality, for the medium of an agent's formal action
consists in its form and act, since every agent acts according to its
actuality, as was said of the passive intellect (Q. 70, A. 1).
Secondly, this opinion is untrue, because in the above explanation,
the active intellect, supposing it to be a separate substance, would
not be joined to us in its substance, but only in its light, as
participated in things understood; and would not extend to the other
acts of the active intellect so as to enable us to understand
immaterial substances; just as when we see colors set off by the sun,
we are not united to the substance of the sun so as to act like the
sun, but its light only is united to us, that we may see the colors.
Thirdly, this opinion is untrue, because granted that, as above
explained, the active intellect were united to us in substance, still
it is not said that it is wholly so united in regard to one
intelligible object, or two; but rather in regard to all intelligible
objects. But all such objects together do not equal the force of the
active intellect, as it is a much greater thing to understand separate
substances than to understand all material things. Hence it clearly
follows that the knowledge of all material things would not make the
active intellect to be so united to us as to enable us by its
instrumentality to understand separate substances.

Fourthly, this opinion is untrue, because it is hardly possible for
anyone in this world to understand all material things: and thus no
one, or very few, could reach to perfect felicity; which is against
what the Philosopher says (Ethic. i, 9), that happiness is a "kind of
common good, co