Concerning the Ten Commandments, which are the Heads of the Law (92-94)

But there are also some people who, without any idea of acquiring gain, do from a bad habit incessantly and inconsiderately swear upon every occasion, even when there is nothing at all about which any doubt is raised, as if they were desirous to fill up the deficiency of their argument with oaths, as if it would not be better to cut their conversation short, or I might rather say to utter nothing at all, but to preserve entire silence, for from a frequency of oaths arises a habit of perjury and impiety.

On which account the man who is going to take an oath ought to investigate everything with care and exceeding accuracy, considering whether the subject is of serious importance, and whether it has really taken place, and whether, if it has, he has comprehended it properly; and considering himself, also, whether he is pure in soul, and body, and tongue, having the first free from all violation of the law, the second from all defilement, and the last from all blasphemy.

For it is an impiety for any disgraceful words to be uttered by that mouth by which the most sacred name is also mentioned.

Let him also consider whether the place and the time are suitable; for before now I have known

some persons, in profane and impure places (in which it is not fitting that mention should be made of either their father or their mother, or of even any old man among their kindred who may have lived a virtuous life), swearing, and stringing together whole sentences full of oaths, using the name of God with all the variety of titles which belong to him, when they should not, out of sheer impiety.