y, through its subject being corrupted. When
therefore a habit has a corruptible subject, and a cause that has a
contrary, it can be corrupted both ways. This is clearly the case with
bodily habits--for instance, health and sickness. But those habits
that have an incorruptible subject, cannot be corrupted indirectly.
There are, however, some habits which, while residing chiefly in an
incorruptible subject, reside nevertheless secondarily in a
corruptible subject; such is the habit of science which is chiefly
indeed in the "possible" intellect, but secondarily in the sensitive
powers of apprehension, as stated above (Q. 50, A. 3, ad 3).
Consequently the habit of science cannot be corrupted indirectly, on
the part of the "possible" intellect, but only on the part of the
lower sensitive powers.

We must therefore inquire whether habits of this kind can be
corrupted directly. If then there be a habit having a contrary,
either on the part of itself or on the part of its cause, it can be
corrupted directly: but if it has no contrary, it cannot be corrupted
directly. Now it is evident that an intelligible species residing in
the "possible" intellect, has no contrary; nor can the active
intellect, which is the cause of that species, have a contrary.
Wherefore if in the "possible" intellect there be a habit caused
immediately by the active intellect, such a habit is incorruptible
both directly and indirectly. Such are the habits of the first
principles, both speculative and practical, which cannot be corrupted
by any forgetfulness or deception whatever: even as the Philosopher
says about prudence (Ethic. vi, 5) that "it cannot be lost by being
forgotten." There is, however, in the "possible" intellect a habit
caused by the reason, to wit, the habit of conclusions, which is
called science, to the cause of which something may be contrary in
two ways. First, on the part of those very propositions which are the
starting point of the reason: for the assertion "Good is not good" is
contrary to the assertion "Good is good" (Peri Herm. ii). Secondly,
on the part of the process of reasoning; forasmuch as a sophistical
syllogism is contrary to a dialectic or demonstrative syllogism.
Wherefore it is clear that a false reason can corrupt the habit of a
true opinion or even of science. Hence the Philosopher, as stated
above, says that "deception is the corruption of science." As to
virtues, some of them are intellectual, residing in reason