Quick answer: Always write could have, should have and would have. “Could of”, “should of” and “would of” are always mistakes.
Why people write “of”
In speech, “could have” is usually shortened to “could’ve”, which sounds almost exactly like “could of”. Writers spell what they hear, but “of” is a preposition and cannot follow a modal verb like could, should, would, must or might.
Examples
| Incorrect | Correct |
|---|---|
| I could of won. | I could have won. |
| You should of called. | You should have called. |
| It would of been fun. | It would have been fun. |
| She must of left. | She must have left. |
Is “could’ve” okay?
Yes. “Could’ve”, “should’ve” and “would’ve” are correct contractions for informal writing. In formal writing, use the full “could have”.
Related guides
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- Its or it’s?The apostrophe rule
Catch this mistake automatically
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Frequently asked questions
Is “should of” ever correct?
Practically never. Unless “of” belongs to the next phrase (“you should, of course, call”), it should be “should have”.
What about “might of”?
Also wrong. Write “might have” or “might’ve”.
Does SpellMistake catch “could of”?
Yes. It flags could of, should of, would of, must of and might of and suggests “have”.