Introduction

(Summa Theologica, I-II, q. 57, a. 5; II-II, q. 47, a. 9.)

As was said above, only that conscience is a safe guide which is not only good—that is, in agreement, as far as one’s efforts can secure this, with the external law—but also certain. A certain conscience is one which, without any prudent fear of erring, judges that a particular act is obligatory or unlawful, and hence here and now to be done or omitted.