‘Conscience’ is a word of which we ought to be I proud. It proclaims that the criterion of good and evil lies within the individual man. Whatever orders he may be called upon to obey, in the last resort a man relies on the interior judgment which says ‘Yes, I ought to act in this way’, or ‘No, it would be sinful to do that.’ Through his conscience, a man is finally accountable to himself alone; or rather, he is freed from that merely human authority under which so many people find themselves.

It was the moralists such as Cic'ero and Seneca who first gave conscience a prominent place, at least in so far as the examination of past actions is concerned. St Paul, who introduced the notion into the Christian tradition, extended it to the control of future actions as well. Here it has no easy part to play, and gives rise to many problems. The scholastic theologians who discussed the extent to which its judgments should be followed, held that it may sometimes be mistaken, for it may consider that something is good which in reality is evil, and vice versa. But it was St Thomas above all who insisted on the authority of conscience, declaring that its ruling must be followed even if it is mistaken, though he added that a man who acts in this way is not necessarily free from blame. The man must obey his erroneous conscience, but in doing so he sins if he could have corrected it; the only solution for him is to alter his conscience by bringing it into agreement with the truth.

The importance given to conscience in St Thomas’s teaching is perhaps most clearly seen in his examination of the conflict that may occur between a subject and his superior.