Usage of preposition "for" while giving explanations

Question

I sometimes come across some texts where the preposition "for" is used to explain reasons. For instance:

• "And K. shook him by the hand, which seemed obviously to surprise him, for he had been going to content himself with a bow."
• "You must let me take your arm, for you are surer of foot than I am."

I have some questions:

• Is this usage common nowadays, or is it outdated? (Both shown examples are from a novel traduced from German to English in 1930).
• Is it more or less formal than "as", "since", and "because"?
• Is it more used in British or American English?
• Finally, how can I apply it correctly so that the sentence is not misunderstood?

Answer 1

This is somewhat antiquated in my experience but would be understood by a native English speaker. The alternatives that you have suggested would be considered normal in contemporary speech and writing. I couldn’t comment on American English though, it may be common usage in some areas. I support here could be a misunderstanding because ‘for’ is typically used to describe purpose e.g. a brush for painting, although I can’t immediately think of a case where there’s clear ambiguity. “Because” is the clearest expression, since ‘as’ is often used when comparing things and ‘since’ can be used to mean ‘after’. “He never walks under ladders since his wife died” for example could be read two different ways.