If I leave, it’s because Bob has arrived.
Does this mean:
Bob has not arrived yet. When Bob does arrive (shortly), I may leave.
Bob is here now and requesting my attention. Therefore, I may leave shortly.
Or is the sentence inherently ambiguous?
Is there a name for this subjunctive–future-tense ambiguity?
MAJOR EDIT: Apparently, this sentence was even more ambigious than I thought!
The situation: I'm chatting online with someone. I say:
"If I leave, it’s because Bob has arrived."
My meaning: when Bob arrives, I will stop chatting with you, and attend to Bob.
My chat partner's interpretation: Bob has already arrived, and, any moment now, you will attend to Bob and stop talking to me.