ance excuses from sin
altogether. For as Augustine says (Retract. i, 9), every sin is
voluntary. Now ignorance causes involuntariness, as stated above (Q.
6, A. 8). Therefore ignorance excuses from sin altogether.

Obj. 2: Further, that which is done beside the intention, is done
accidentally. Now the intention cannot be about what is unknown.
Therefore what a man does through ignorance is accidental in human
acts. But what is accidental does not give the species. Therefore
nothing that is done through ignorance in human acts, should be
deemed sinful or virtuous.

Obj. 3: Further, man is the subject of virtue and sin, inasmuch as he
is partaker of reason. Now ignorance excludes knowledge which
perfects the reason. Therefore ignorance excuses from sin altogether.

_On the contrary,_ Augustine says (De Lib. Arb. iii, 18) that "some
things done through ignorance are rightly reproved." Now those things
alone are rightly reproved which are sins. Therefore some things done
through ignorance are sins. Therefore ignorance does not altogether
excuse from sin.

_I answer that,_ Ignorance, by its very nature, renders the act which
it causes involuntary. Now it has already been stated (AA. 1, 2) that
ignorance is said to cause the act which the contrary knowledge would
have prevented; so that this act, if knowledge were to hand, would be
contrary to the will, which is the meaning of the word involuntary.
If, however, the knowledge, which is removed by ignorance, would not
have prevented the act, on account of the inclination of the will
thereto, the lack of this knowledge does not make that man unwilling,
but not willing, as stated in _Ethic._ iii, 1: and such like
ignorance which is not the cause of the sinful act, as already
stated, since it does not make the act to be involuntary, does not
excuse from sin. The same applies to any ignorance that does not
cause, but follows or accompanies the sinful act.

On the other hand, ignorance which is the cause of the act, since it
makes it to be involuntary, of its very nature excuses from sin,
because voluntariness is essential to sin. But it may fail to excuse
altogether from sin, and this for two reasons. First, on the part of
the thing itself which is not known. For ignorance excuses from sin,
in so far as something is not known to be a sin. Now it may happen
that a person ignores some circumstance of a sin, the knowledge of
which circumstance would prevent him from sinning, whe