riance with erring reason.

_On the contrary,_ As stated in the First Part (Q. 79, A. 13),
conscience is nothing else than the application of knowledge to some
action. Now knowledge is in the reason. Therefore when the will is at
variance with erring reason, it is against conscience. But every such
will is evil; for it is written (Rom. 14:23): "All that is not of
faith"--i.e. all that is against conscience--"is sin." Therefore the
will is evil when it is at variance with erring reason.

_I answer that,_ Since conscience is a kind of dictate of the reason,
for it is an application of knowledge to action, as was stated in
the First Part (Q. 19, A. 13), to inquire whether the will is evil
when it is at variance with erring reason, is the same as to inquire
"whether an erring conscience binds." On this matter, some
distinguished three kinds of actions: for some are good generically;
some are indifferent; some are evil generically. And they say that if
reason or conscience tell us to do something which is good
generically, there is no error: and in like manner if it tell us not
to do something which is evil generically; since it is the same
reason that prescribes what is good and forbids what is evil. On the
other hand if a man's reason or conscience tells him that he is bound
by precept to do what is evil in itself; or that what is good in
itself, is forbidden, then his reason or conscience errs. In like
manner if a man's reason or conscience tell him, that what is
indifferent in itself, for instance to raise a straw from the ground,
is forbidden or commanded, his reason or conscience errs. They say,
therefore, that reason or conscience when erring in matters of
indifference, either by commanding or by forbidding them, binds: so
that the will which is at variance with that erring reason is evil
and sinful. But they say that when reason or conscience errs in
commanding what is evil in itself, or in forbidding what is good in
itself and necessary for salvation, it does not bind; wherefore in
such cases the will which is at variance with erring reason or
conscience is not evil.

But this is unreasonable. For in matters of indifference, the will
that is at variance with erring reason or conscience, is evil in some
way on account of the object, on which the goodness or malice of the
will depends; not indeed on account of the object according as it is
in its own nature; but according as it is accidentally apprehended by
reaso