A simple subject is probably the most basic unit in sentence construction. A subject is a noun, which is a person, place, thing, or idea. A subject tells us who or what the sentence is going to be about. Without a subject, we cannot have a complete sentence. A simple subject is a subject that has just one noun as the focus of the sentence. This means that only one noun does the action, or connects, to the verb of the sentence. Hope I helped u.. Plzz mark as the BRAINLIEST answer..