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.

Therefore sin cannot be alleviated by any ignorance, but only by such
as is a cause of the sin being committed, and yet does not excuse
from the sin altogether. Now it happens sometimes that such like
ignorance is directly and essentially voluntary, as when a man is
purposely ignorant that he may sin more freely, and ignorance of this
kind seems rather to make the act more voluntary and more sinful,
since it is through the will's intention to sin that he is willing to
bear the hurt of ignorance, for the sake of freedom in sinning.
Sometimes, however, the ignorance which is the cause of a sin being
committed, is not directly voluntary, but indirectly or accidentally,
as when a man is unwilling to work hard at his studies, the result
being that he is ignorant, or as when a man willfully drinks too much
wine, the result being that he becomes drunk and indiscreet