subject The part of a clause that identifies who or what is being discussed.
verb A word or phrase that expresses action or being and, along with a subject, is a basic component of a sentence.
object The part of a clause that receives the action of the verb, or the part of a phrase that follows a preposition: At the checkpoint, we unloaded the canoes.
A comma that separates two of a sentence’s core elements—subject, verb, and object—confuses matters by suggesting that some other material has been added.