THE SOUL.--Our soul is immaterial and more complete than that of
animals, for St. Thomas does not formally deny that animals have souls; the
instinct of animals is the sensitive soul according to Aristotle, which is
capable of four faculties: sensibility, imagination, memory, and
estimation, that is elementary intelligence: "The bird picks up straw, not
because it gratifies her feelings [not by a movement of sensibility], but
because it serves to make her nest. It is therefore necessary that an
animal should perceive those intuitions which do not come within the scope
of the senses. It is by opinion or estimation that it perceives these
intuitions, these distant ends." We, mankind, possess a soul which is
sensibility, imagination, memory, and reason. Reason is the faculty not
only of having ideas, but of establishing connections and chains of
connection between the ideas and of conceiving general ideas. Reason pauses
before reaching God because the idea of God precisely is the only one which
cannot be brought to the mind by the interrelation of ideas, for God
surpasses all ideas; the idea of God is given by faith, which can be
subsequently helped by reason, for the latter can work to make faith
perceptible to reason.

Our soul is full of passions, divisible into two great categories, the
passions of desire and those of anger. The passions of desire are rapid or
violent movements towards some object which seems to us a good; the
passions of anger are movements of revolt against something which opposes
our movement towards a good. The common root of all the passions is love,
for it is obvious that from it are derived the passions of desire; and as
for the passions of wrath they would not exist if we had no love of
anything, in which case our desire not coming into collision would not turn
into revolt against the obstacle. We are free to do good or evil, to master
our evil passions and to follow those of which reason approves. Here