What is the difference between a simple and a complete subject?

Hint: The entity, location, object, or idea doing or being is the subject of a sentence. The topic of a sentence or clause is often referred to as the "naming element." It identifies the subject of the sentence or the person or thing who or what is performing an action in the sentence. Most of the time, the subject is a verb, pronoun, or noun phrase.

Complete answer:
Since we know what is a subject, let us understand what is a simple and a complete subject.

Simple Subject: There is a subject and a predicate in every sentence. The simple subject identifies who or what is performing an action. There are no other words that define or change the subject noun or pronoun.

Example of simple subject:
Cockroaches scare me.
In this sentence, ‘cockroaches’ are ‘doing’ the verb, ‘scare.’
‘Cockroaches’ is the simple subject.

Complete Subject: The simple subject, or the key word or words in a subject, including any modifiers that may define the subject, makes up a complete subject. Ask yourself who or what executes the action in the sentence to determine the complete subject.

Example of complete subject:
Four cardboard boxes remained in the empty house.
In this sentence, ‘boxes’ are ‘doing’ the verb, ‘remained.’
Modifiers to ‘boxes’ include ‘four cardboard.’
‘Four cardboard boxes’ is the complete subject.

A simple subject, without any modifiers, is a main word or words that say what or what a sentence is about. Whereas, many of the words that say what or whom a sentence is about, including any modifiers, make up a complete subject.

Note: A compound subject is a statement that has two or more subjects. "And" or "or" and, perhaps, a sequence of commas join compound subjects. There are several different ways to vary these sentence structures in the compound subject.