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 ), 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:
A Whether ignorance is a cause of sin?
A Whether ignorance is a sin?
A Whether it excuses from sin altogether?
A Whether it diminishes sin?