4 And how, I will explain; for this is the paradox. He who has sworn that he would flog the man-servant or maid-servant, yet has afterwards been prohibited from this, has perjured himself, not having done what he has sworn to do: and also, he has involved in the crime of perjury the party forbidding and hindering the oath from being kept. For not only they who take a false oath, but they who impose that necessity on others, are liable to the same accusation. And not merely in houses, but also in the forum we may see that this takes place; and especially in fights, when those who box with one another swear things that are contrary.
One swears that he will beat, the other that he will not be beaten. One swears that he will carry off the cloak, the other that he will not suffer this. One that he will exact the money, the other that he will not pay it. And many other such contradictory things, those who are contentious take an oath to do. So also in shops, and in schools, it may generally be observed that the same thing occurs. Thus the workman has often sworn that he will not suffer his apprentice to eat or drink, before he has finished all his assigned task.
And so also the pedagogue has often acted towards a youth; and a mistress towards her maid-servant; and when the evening has overtaken them, and the work has remained unfinished, it is necessary either that those who have not executed their task should perish with hunger, or that those who have sworn should altogether forswear themselves. For that malignant demon, who is always lying in wait against our blessings, being present and hearing the obligation of the oaths, impels those who are answerable to indifference; or works some other difficulty; so that the task being unperformed, blows, insults, and perjuries, and a thousand other evils, may take place.
And just as when children drag with all their might a long and rotten cord in directions opposite to each other; if the cord snaps in the middle, they all fall flat upon their backs, and some strike their heads, and some another part of the body; so also they who each engage with an oath to perform things that are contrary, when the oath is broken by the necessity of the case, both parties fall into the same gulf of perjury: these by actually perjuring themselves, and those by affording the occasion of perjury to the others.
Source: Homilies on the Statues (New Advent)