distinct powers. For the same
power of the soul regards both sides of a contrariety, as sight
regards both black and white, according to the Philosopher (De Anima
ii, 11). But suitable and harmful are contraries. Since, then, the
concupiscible power regards what is suitable, while the irascible is
concerned with what is harmful, it seems that irascible and
concupiscible are the same power in the soul.

Obj. 2: Further, the sensitive appetite regards only what is suitable
according to the senses. But such is the object of the concupiscible
power. Therefore there is no sensitive appetite differing from the
concupiscible.

Obj. 3: Further, hatred is in the irascible part: for Jerome says on
Matt. 13:33: "We ought to have the hatred of vice in the irascible
power." But hatred is contrary to love, and is in the concupiscible
part. Therefore the concupiscible and irascible are the same powers.

_On the contrary,_ Gregory of Nyssa (Nemesius, De Natura Hominis) and
Damascene (De Fide Orth. ii, 12) assign two parts to the sensitive
appetite, the irascible and the concupiscible.

_I answer that,_ The sensitive appetite is one generic power, and
is called sensuality; but it is divided into two powers, which are
species of the sensitive appetite--the irascible and the
concupiscible. In order to make this clear, we must observe that in
natural corruptible things there is needed an inclination not only to
the acquisition of what is suitable and to the avoiding of what is
harmful, but also to resistance against corruptive and contrary
agencies which are a hindrance to the acquisition of what is
suitable, and are productive of harm. For example, fire has a natural
inclination, not only to rise from a lower position, which is
unsuitable to it, towards a higher position which is suitable, but
also to resist whatever destroys or hinders its action. Therefore,
since the sensitive appetite is an inclination following sensitive
apprehension, as natural appetite is an inclination following the
natural form, there must needs be in the sensitive part two appetitive
powers--one through which the soul is simply inclined to seek what is
suitable, according to the senses, and to fly from what is hurtful,
and this is called the concupiscible: and another, whereby an animal
resists these attacks that hinder what is suitable, and inflict harm,
and this is called the irascible. Whence we say that its object is
something arduous, because its tenden