How frequent is “for” used to mean “because”?

Question

In this question is the sentence

The city must have been prosperous, for it enjoyed a high level of civilization.

Although I understand the meaning, I must admit I never realized "for" could be used as "because", which I discovered in an online dictionnary. I also don't remember any lesson about it in school (but I basically only had a few hours a week in secondary school and then learned by myself, so this might explain that). Therefore I was wondering if it can replace "because" in any occasion and any level of speach or if there were "rules" indicating you should use one rather than the other (or even forbidding to use it)?

Answer 1

I can't think of any way to establish how frequently for is used in the sense of because or because of.

Being shorter, for is likely to be used more often, especially in conversation.

Note, however, that the two words are not always interchangeable and the choice will often depend on the context.

While you can say either:

We are staying at home because rain is expected this afternoon
or
We are staying at home for rain is expected this afternoon

You can't use for at the start of a sentence to mean because:

Because he broke his leg, he is confined to his house.
NOT: >For he broke his leg, he is confined to his house.

Although you can use it if you reverse the sentence:

He is confined to his house for he broke his leg.