g easily or difficultly lost. As to natural
qualities, some regard a thing in the point of its being in a state
of potentiality; and thus we have the second species of quality:
while others regard a thing which is in act; and this either deeply
rooted therein or only on its surface. If deeply rooted, we have the
third species of quality: if on the surface, we have the fourth
species of quality, as shape, and form which is the shape of an
animated being." But this distinction of the species of quality seems
unsuitable. For there are many shapes, and passion-like qualities,
which are not natural but adventitious: and there are also many
dispositions which are not adventitious but natural, as health,
beauty, and the like. Moreover, it does not suit the order of the
species, since that which is the more natural is always first.

Therefore we must explain otherwise the distinction of dispositions
and habits from other qualities. For quality, properly speaking,
implies a certain mode of substance. Now mode, as Augustine says
(Gen. ad lit. iv, 3), "is that which a measure determines": wherefore
it implies a certain determination according to a certain measure.
Therefore, just as that in accordance with which the material
potentiality (_potentia materiae_) is determined to its substantial
being, is called quality, which is a difference affecting the
substance, so that, in accordance with the potentiality of the
subject is determined to its accidental being, is called an
accidental quality, which is also a kind of difference, as is clear
from the Philosopher (Metaph. v, text. 19).

Now the mode o[r] determination of the subject to accidental being
may be taken in regard to the very nature of the subject, or in
regard to action, and passion resulting from its natural principles,
which are matter and form; or again in regard to quantity. If we take
the mode or determination of the subject in regard to quantity, we
shall then have the fourth species of quality. And because quantity,
considered in itself, is devoid of movement, and does not imply the
notion of good or evil, so it does not concern the fourth species of
quality whether a thing be well or ill disposed, nor quickly or
slowly transitory.

But the mode o[r] determination of the subject, in regard to action
or passion, is considered in the second and third species of quality.
And therefore in both, we take into account whether a thing be done
with ease or difficulty; w