of knowledge perfecting the reason that forbids the
act of sin, in so far as it directs human acts.

Now we must observe that the reason directs human acts in accordance
with a twofold knowledge, universal and particular: because in
conferring about what is to be done, it employs a syllogism, the
conclusion of which is an act of judgment, or of choice, or an
operation. Now actions are about singulars: wherefore the conclusion
of a practical syllogism is a singular proposition. But a singular
proposition does not follow from a universal proposition, except
through the medium of a particular proposition: thus a man is
restrained from an act of parricide, by the knowledge that it is
wrong to kill one's father, and that this man is his father. Hence
ignorance about either of these two propositions, viz. of the
universal principle which is a rule of reason, or of the particular
circumstance, could cause an act of parricide. Hence it is clear that
not every kind of ignorance is the cause of a sin, but that alone
which removes the knowledge which would prevent the sinful act.
Consequently if a man's will be so disposed that he would not be
restrained from the act of parricide, even though he recognized his
father, his ignorance about his father is not the cause of his
committing the sin, but is concomitant with the sin: wherefore such a
man sins, not "through ignorance" but "in ignorance," as the
Philosopher states (Ethic. iii, 1).

Reply Obj. 1: Non-being cannot be the direct cause of anything: but
it can be an accidental cause, as being the removal of an impediment.

Reply Obj. 2: As knowledge, which is removed by ignorance, regards
sin as turning towards something, so too, ignorance of this respect
of a sin is the cause of that sin, as removing its impediment.

Reply Obj. 3: The will cannot turn to that which is absolutely
unknown: but if something be known in one respect, and unknown in
another, the will can will it. It is thus that ignorance is the cause
of sin: for instance, when a man knows that what he is killing is a
man, but not that it is his own father; or when one knows that a
certain act is pleasurable, but not that it is a sin.
________________________

SECOND ARTICLE [I-II, Q. 76, Art. 2]

Whether Ignorance Is a Sin?

Objection 1: It would seem that ignorance is not a sin. For sin is "a
word, deed or desire contrary to God's law," as stated above (Q. 71,
A. 5). Now ignorance does not denote an act, eit