I have seen a discussion of double gerunds and subject-verb agreement, but not addressing the following specific situtation:
"Reading and studying history HAS or HAVE been formative...": two gerunds with the same object as the subject of the sentence. I think a singular verb is clearly called for. Arguments in favor or against?
It depends entirely on context and whether or not you are using the two things individually or referring to a single collective thing.
The sentence you provided is ambiguous but you can make the meaning clear (either way) by slightly rephrasing it.
For instance:
Both reading and studying history have been formative.
The activity of reading and studying history has been formative.
Without rephrasing it, an argument could be made for either the singular or the plural. It depends on what you're trying to express. Neither would necessarily be wrong.
