Is should of correct?

Question:

I often see the spelling should of, as in the following sentence:

• I should of studied longer for my English test.

Is this correct?

Answer:

No, the spelling should of is non-standard English. The correct spelling is should've, an informal contraction for the verb phrase should have. So the sentence should read as follows:

• I should've (or should have) studied longer for my English test.

The same is true for the contractions would've, could've, might've and must've (or, in formal writing, would have, could have, might have and must have).