Why "should of" shouldn’t be: the grammar mistake explained

What kind of error is it?

grammatical error

Why do people make this mistake?

The error is a result of the incorrect transcription of the spoken contraction "should've", which sounds very similar to "should of". People often misunderstand the contraction "should've" (short for "should have") and write it as "should of" due to the similar pronunciation.

What is correct?

The correct form is "should have", where "have" is the auxiliary verb used to form the perfect aspect.