When to use have or of?

Answer 1

Basic Idea:It is a very common mistake to say things like 'could of', 'should of', 'might of', or 'would of'. When talking with friends this isn't so bad, but in written English or in more formal settings, it sounds very bad. You should say 'could have', should have', might have' or 'would have'. They can be abbreviated with 've when writing dialogue or when quoting someone, as in should've. The abbreviation is probably what leads to the 'of' error. In the cases above, the word have is a helping verb; it helps to clarify the verb's tense. "If I had known that you were coming, I would have baked a cake." At that past time, I did not know that you were coming. But if I HAD known [had is the past tense of have], if I could go back and change the past, I would have baked a cake. The word 'of' is never used to help express a verb's tense. Check the link for a helpful site on helping verbs!

[NOTE: NOT for the faint of heart. If the above is enough, you should go to your next question.]

You might ask if it would be ok to say "If I knew you were coming, I would have baked a cake." The difference is subtle. Saying "If I knew" implies that perhaps I knew, and perhaps I did not; it is unclear to me at this time whether or not I knew. And that might be exactly what you want to say. But if you are interested in the clearest language this leads to a logical conflict, doesn't it? It is unclear to me at this time whether or not I knew you were coming, but we can use the baking of a cake as a partial proof. If no cake was baked, then certainly I did not know you were coming. Assuming for a moment there was no cake, I am saying that I'm certain I did not know, but I'm expressing it with a verb that implies uncertainty. If a cake was baked, there is still ambiguity. "If I had known" implies that I in fact did not know, but would have taken action if I had.

Answer 2

Use "have" to show possession or ownership, to form the present perfect tense, or as a helping verb with another verb. Use "of" to indicate a relationship or connection between two things or to show origin or source, but be careful not to confuse it with the verb "have."