We must now consider the causes of sin, in particular, and (1) The internal causes of sin; (2) its external causes; and (3) sins which are the causes of other sins. In view of what has been said above (A. 2), the first consideration will be threefold: so that in the first place we shall treat of ignorance, which is the cause of sin on the part of reason; secondly, of weakness or passion, which is the cause of sin on the part of the sensitive appetite; thirdly, of malice, which is the cause of sin on the part of the will.
Under the first head, there are four points of inquiry:
(1) Whether ignorance is a cause of sin?
(2) Whether ignorance is a sin?
(3) Whether it excuses from sin altogether?
(4) Whether it diminishes sin? ________________________
FIRST ARTICLE [I-II, Q. 76, Art. 1]
Whether Ignorance Can Be a Cause of Sin?
Objection 1: It would seem that ignorance cannot be a cause of sin: because a non-being is not the cause of anything. Now ignorance is a non-being, since it is a privation of knowledge. Therefore ignorance is not a cause of sin.
Obj. 2: Further, causes of sin should be reckoned in respect of sin
being a turning to something, as was stated above (Q. 75, A. 1).
Now ignorance seems to savor of turning away from something.
Therefore it should not be reckoned a cause of sin.