Could of, Would of, Should of

When people say such things as, “I could have fainted,” “She should have called,” or “We would have gone,” they usually contract the pronunciation of have. The contracted forms are could’ve, might’ve, should’ve, and so on. To many ears, the contracted have sounds like of, and so people sometimes write, “I could of fainted,” “She might of called,” and “We would of gone.” This is a misunderstanding of the syntax: of is a preposition and can’t serve in place of an auxiliary verb.