Whether all perjury is sinful?

❌ Objection 1 : It would seem that not all perjury is sinful. Whoever does not fulfil what he has confirmed on oath is seemingly a perjurer. Yet sometimes a man swears he will do something unlawful (adultery, for instance, or murder): and if he does it, he commits a sin. If therefore he would commit a sin even if he did it not, it would follow that he is perplexed.

❌ Objection 2 : Further, no man sins by doing what is best. Yet sometimes by committing a perjury one does what is best: as when a man swears not to enter religion, or not to do some kind of virtuous deed. Therefore not all perjury is sinful.

❌ Objection 3 : Further, he that swears to do another's will would seem to be guilty of perjury unless he do it. Yet it may happen sometimes that he sins not, if he do not the man's will: for instance, if the latter order him to do something too hard and unbearable. Therefore seemingly not all perjury is sinful.

❌ Objection 4 : Further, a promissory oath extends to future, just as a declaratory oath extends to past and present things. Now the obligation of an oath may be removed by some future occurrence: thus a state may swear to fulfil some obligation, and afterwards other citizens come on the scene who did not take the oath; or a canon may swear to keep the statutes of a certain church, and afterwards new statutes are made. Therefore seemingly he that breaks an oath does not sin.