Given the following example sentence:
The secondary effect of ability X and ability Y has been reworked.
I'm not really sure what to make of the subject-verb agreement here.
In this case, is the subject truly the singular "secondary effect"?
Or should this be read as "secondary effect of ability X and [secondary effect of] ability Y" and thus take a plural verb?
It occurs to me that the easy answer is that the sentence probably should be rewritten to be unambiguous, i.e.
The secondary effects of ability X and ability Y have been reworked.
But this makes me wonder if "secondary effect of ability X and ability Y" is even grammatical in the first place, given that the secondary effects of each ability are distinct.
Is the subject singular or plural?
Is the subject even grammatically correct to begin with?