English: contractions

Self-tutoring about English: the tutor mentions an idea his wife mightn’t appreciate.

I’ve heard of could’ve…what about couldn’t’ve? I’ve never seen it in print, but why not, in casual writing?

In formal writing – essays, for instance – I was always told that contractions are forbidden, anyway: you can’t use can’t in an essay. However, I can’t be sure what a creative writing instructor might say.

I can guess what my wife will say about couldn’t’ve – that I couldn’t’ve pretended she’d be fine with it.