Is there such a thing as a compound conjunction like shouldn’t’ve or I’d’ve?
Not according to formal grammar, although people do it in spoken informal English all the time (at least around here).
I think you mean compound contraction.
:smack:
I do it in informal writing, too, but mostly for the novelty. I’ve probably used them in posts on here, for example.
I’d say they are a reasonable approximation of casual speech, and I’m liable to pronounce that /shUd n@v/ (“should-nuv”, more or less), two syllables. So I don’t see any reason why you shouldn’t use them in informal writing (and I do it from time to time myself), if you’re looking to give it a conversational feel. Obviously they’re right out in formal writing, since even the well-worn single contractions aren’t permitted there.