causes may be considered in
two ways: first, from the point of view of their species or nature,
as fire differs from water; secondly, from the point of view of the
difference in their active power. In the passions of the soul we can
treat the difference of their active or motive causes in respect of
their motive power, as if they were natural agents. For every mover,
in a fashion, either draws the patient to itself, or repels it from
itself. Now in drawing it to itself, it does three things in the
patient. Because, in the first place, it gives the patient an
inclination or aptitude to tend to the mover: thus a light body,
which is above, bestows lightness on the body generated, so that it
has an inclination or aptitude to be above. Secondly, if the
generated body be outside its proper place, the mover gives it
movement towards that place. Thirdly, it makes it to rest, when it
shall have come to its proper place: since to the same cause are due,
both rest in a place, and the movement to that place. The same
applies to the cause of repulsion.

Now, in the movements of the appetitive faculty, good has, as it
were, a force of attraction, while evil has a force of repulsion. In
the first place, therefore, good causes, in the appetitive power, a
certain inclination, aptitude or connaturalness in respect of good:
and this belongs to the passion of _love:_ the corresponding contrary
of which is _hatred_ in respect of evil. Secondly, if the good be not
yet possessed, it causes in the appetite a movement towards the
attainment of the good beloved: and this belongs to the passion of
_desire_ or _concupiscence:_ and contrary to it, in respect of evil,
is the passion of _aversion_ or _dislike._ Thirdly, when the good is
obtained, it causes the appetite to rest, as it were, in the good
obtained: and this belongs to the passion of _delight_ or _joy;_ the
contrary of which, in respect of evil, is _sorrow_ or _sadness._

On the other hand, in the irascible passions, the aptitude, or
inclination to seek good, or to shun evil, is presupposed as arising
from the concupiscible faculty, which regards good or evil absolutely.
And in respect of good not yet obtained, we have _hope_ and _despair._
In respect of evil not yet present we have _fear_ and _daring._ But in
respect of good obtained there is no irascible passion: because it is
no longer considered in the light of something arduous, as stated
above (A. 3). But evil already present gi