could have done / would have done / should have done: I ………………….(buy) bread but I didn’t know we needed it. (past possibility)
could have bought
could have done / would have done / should have done: We ……………….(invite) so many people to our party! I’m worried that we won’t have enough room for everyone. (past negative advice / regret)
shouldn’t have invited
could have done / would have done / should have done: We ……………….(join) you at the restaurant, but we couldn’t get a babysitter. (past willingness)
would have joined