- It’s never correct to write would of, should of, or could of.
- The correct forms are would have, should have, and could have.
When spoken aloud, would of and its fellows should of and could of sound exactly like would’ve, could’ve and should’ve. But even if no one can tell the difference when you’re speaking, the mistake becomes obvious as soon as you write it down.
The Right Way to Spell Would of, Should of, and Could of
When people write would of, should of, could of, will of or might of, they are usually confusing the verb have with the preposition of. So would of is would have, could of is could have, should of is should have, will of is will have, and might of is might have:
This common mistake is likely caused by the similar pronunciation of the words of and have, especially when have is contracted, as in should’ve. This mistake also happens with the negations of modal verbs:
from Grammarly Blog https://www.grammarly.com/blog/would-of-could-of-should-of/