Why are vulgar words often called swear words

Question

When I say ‘I swear I will do it by today’ I mean ‘I promise I will do it by today’ I dont mean anything vulgar. Yet, when I see people using the term swear, they mean those vulgar words. When and why did this shift happen?

In: 79

Answer 1

https://en.wiktionary.org/wiki/swear#Etymology_1

> The sense “to use bad language” developed in Middle English and is based on the Christian prohibition against swearing in general (cf. Matthew 5:33-37) and invoking God’s name in particular (i.e. frequent swearing was considered similar to the use of obscene words).

So “swearing” was not allowed since it was considered sacrilegious, and so it became a euphemism for using any kind of bad language.