Aquinas on Self-Knowledge

Aquinas distinguishes two kinds of self-knowledge.
The intellect, he says, knows itself 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. (ST I, 87, 1)
Although the second kind of knowledge about the
nature or essence of man raises interesting issues, in this
paper I want to consider just one thesis ascribed to
Aquinas as concerns the first kind of self-knowledge in
which the intellect knows its own mental states (hereafter
self-knowledge simpliciter). This is the thesis that what
distinguishes human beings from animals is 'a selfreflexive
power that allows them to have not only
cognitions but also cognition of the truth of their
cognitions'. (MacDonald 1993, 186) Call this the M-thesis.
One interpretation of the M-thesis might seem trivial: what
distinguishes humans from non-rational animals is not
merely the fact that they are able to have concepts and
produce thoughts on the basis of the concepts that they
possess but also that the indispensable precondition of
being a person is precisely the fact of human selfknowledge.
For what use would our concepts and thinking
be if we did not know what concepts we are having or what
thoughts we are entertaining?