Would of, could of, and should of are mistakes. Have you ever found yourself writing any of these?
Of and have sound similar when we say them out loud. This is especially true when we use the contractions would've, could've, and should've. Don't get tricked! Have (or 've) is the correct choice.
I would of called you, but I lost your number.
I could of danced all night.
I should of ordered a salad.
I would've called you, but I lost your number.
I could've danced all night.
I should've ordered a salad.
Why is of a mistake?
Would, could, and should are helping verbs that need to be a part of something called a verb phrase. Verb phrases are made up of one or more helping verbs and a main verb. Have can function as a helping verb. Of can't.
In our incorrect sentences, would, could, and should are followed by the word of, which is hopelessly trying to be a helping verb. But no matter how hard it tries, of is limited by its definition and function. The word that people mean to use here is the verb have.
The verb phrases in our example sentences are would have called, could have danced, and should have ordered. Would, could, should, and have are helping verbs. Called, danced, and ordered are main verbs.