A simple subject is the main noun a sentence is about, while a complete subject consists of all the words a sentence is about. For example, in the sentence, "The brown dog chews a bone," the simple subject is "dog," while the complete subject is "the brown dog."
The complete subject includes all other words that describe or modify the simple subject, including other nouns. In the example, "The old brown dog wearing a collar chews a bone," the complete subject is "the old brown dog wearing a collar." The simple subject remains "dog."
The simple subject is always a single noun or pronoun. When no descriptive words appear, the simple and complete subjects are the same, such as in the sentence, "Pete eats a hot dog," where both subjects are "Pete."
Simple and complete subjects operate the same as simple and complete predicates, where the simple predicate is the main verb and the complete predicate is the verb and all the words it modifies. For example, in the sentence, "Pete eats a hot dog," the simple predicate is "eats," while the complete predicate is "eats a hot dog."
In some complex sentences, identifying the complete subject and the complete predicate is more difficult. For example, in the sentence, "The dog, who is brown, wears a red collar," the phrase "who is brown" is part of the complete subject.