Reply Obj. 2: So far as voluntariness remains in the ignorant person, the intention of sin remains in him: so that, in this respect, his sin is not accidental.
Reply Obj. 3: If the ignorance be such as to exclude the use of reason entirely, it excuses from sin altogether, as is the case with madmen and imbeciles: but such is not always the ignorance that causes the sin; and so it does not always excuse from sin altogether. ________________________
FOURTH ARTICLE [I-II, Q. 76, Art. 4]
Whether Ignorance Diminishes a Sin?
Objection 1: It would seem that ignorance does not diminish a sin. For that which is common to all sins does not diminish sin. Now ignorance is common to all sins, for the Philosopher says (Ethic. iii, 1) that "every evil man is ignorant." Therefore ignorance does not diminish sin.
Obj. 2: Further, one sin added to another makes a greater sin. But ignorance is itself a sin, as stated above (A. 2). Therefore it does not diminish a sin.
Obj. 3: Further, the same thing does not both aggravate and diminish sin. Now ignorance aggravates sin; for Ambrose commenting on Rom. 2:4, "Knowest thou not that the benignity of God leadeth thee to penance?" says: "Thy sin is most grievous if thou knowest not." Therefore ignorance does not diminish sin.
Obj. 4: Further, if any kind of ignorance diminishes a sin, this would seem to be chiefly the case as regards the ignorance which removes the use of reason altogether. Now this kind of ignorance does not diminish sin, but increases it: for the Philosopher says (Ethic. iii, 5) that the "punishment is doubled for a drunken man." Therefore ignorance does not diminish sin.
On the contrary, Whatever is a reason for sin to be forgiven, diminishes sin. Now such is ignorance, as is clear from 1 Tim. 1:13: "I obtained . . . mercy . . . because I did it ignorantly." Therefore ignorance diminishes or alleviates sin.
I answer that, Since every sin is voluntary, ignorance can diminish sin, in so far as it diminishes its voluntariness; and if it does not render it less voluntary, it nowise alleviates the sin. Now it is evident that the ignorance which excuses from sin altogether (through making it altogether involuntary) does not diminish a sin, but does away with it altogether. On the other hand, ignorance which is not the cause of the sin being committed, but is concomitant with it, neither diminishes nor increases the sin.