Forswear

The irregular verb 'to forswear' is a development of swear, made with the prefix for-. This has many meanings and shades of meaning, which no doubt has influenced the fact that forswear has several conflicting uses. It is rarely used these days, perhaps for the same reason; but you may find it in all sorts of older texts. The main meanings you may come across are:

• To abandon something by taking an oath, or promising solemnly, not to do it. This is perhaps the most common sense nowadays: "I have forsworn tobacco" means 'I have given up tobacco - honestly; I promise.'
• To swear that something is not true; for example, a gambler who forswears a debt is denying that the debt was ever incurred.
• To be forsworn is 'not to do something having promised to do it', 'to go back on one's word', or 'to fail in what one has sworn to do'.
• To commit perjury.

You should notice that these are very different. That is one good reason not to use the word; and one to be very careful when you meet it in another's writing.

'To forswear' is an irregular verb. Its forms are given here:

Base form	past tense	-ed participle	Remarks
forswear	forswore	forsworn

This is one of the "the 250 or so irregular verbs" listed in Quirk 1985. The list "contains most of the irregular verbs in present-day English ... but is not meant to be exhaustive, particularly with regard to derivative verbs." AWE has copied most of the entries in that list. The verb 'to forswear' belongs to Quirk's Class 4 A b.