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 [1765] (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:

A1 Whether ignorance is a cause of sin?

A2 Whether ignorance is a sin?

A3 Whether it excuses from sin altogether?

A4 Whether it diminishes sin?