: "Let the mind strive not to see
itself as if it were absent, but to discern itself as present"--i.e.
to know how it differs from other things; which is to know its
essence and nature.

Reply Obj. 1: The mind knows itself by means of itself, because at
length it acquires knowledge of itself, though led thereto by its own
act: because it is itself that it knows, since it loves itself, as he
says in the same passage. For a thing can be called self-evident in
two ways, either because we can know it by nothing else except
itself, as first principles are called self-evident; or because it is
not accidentally knowable, as color is visible of itself, whereas
substance is visible by its accident.

Reply Obj. 2: The essence of an angel is an act in the genus of
intelligible things, and therefore it is both intellect and the thing
understood. Hence an angel apprehends his own essence through itself:
not so the human mind, which is either altogether in potentiality to
intelligible things--as is the passive intellect--or is the act of
intelligible things abstracted from the phantasms--as is the active
intellect.

Reply Obj. 3: This saying of the Philosopher is universally true in
every kind of intellect. For as sense in act is the sensible in act,
by reason of the sensible likeness which is the form of sense in act,
so likewise the intellect in act is the object understood in act, by
reason of the likeness of the thing understood, which is the form of
the intellect in act. So the human intellect, which becomes actual by
the species of the object understood, is itself understood by the
same species as by its own form. Now to say that in "things without
matter the intellect and what is understood are the same," is equal
to saying that "as regards things actually understood the intellect
and what is understood are the same." For a thing is actually
understood in that it is immaterial. But a distinction must be drawn:
since the essences of some things are immaterial--as the separate
substances called angels, each of which is understood and
understands, whereas there are other things whose essences are not
wholly immaterial, but only the abstract likenesses thereof. Hence
the Commentator says (De Anima iii) that the proposition quoted is
true only of separate substances; because in a sense it is verified
in their regard, and not in regard of other substances, as already
stated (Reply Obj. 2).
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