Rhetoric and Composition/Parts of the Sentence

Parts of the Sentence

English Language sentences typically have four parts: subject, predicate, complement, and modifers. The examples which follow are of necessity somewhat oversimplified—there are many gray areas of definition and usage—but they illustrate some basic principles.

Subject

The subject of a sentence is a noun or pronoun. In active-voice sentences it is the noun performing the action in the sentence:

The boy crossed the street.
My mother works in the city.
Mark is really cool.

Predicate

The predicate in the sentence is the verb or verb phrase, linked to the subject, that tells what action is being performed.

The boy crossed the street.
My mother works in the city.
Robbo plays the drums.
Mark plays better than Robbo.

Note: Forms of the verb "to be" (am, is, are, was, were, ____ be, _____ been) are sometimes used by themselves as predicates ("The boy was tall") and sometimes used as tense or mood indicators in a verb phrase ("We should be arriving soon.") Forms of the verb to be are tricky because they are often unobtrusive and they don't show action, which is what we normally expect of verbs. They belong to category of verbs known as linking verbs because they serve as the verbal equivalent of an equals sign in math. (The house is green. She seems angry. The burden became excessive.)

Complement

Some subject-predicate combinations make sense all by themselves. (John smiled. My pet fish died.) Some subject-predicate combinations are incomplete until a noun or adjective is supplied which completes the meaning begun by the subject and predicate. The word "complement" is a noun form based on the verb "complete." In essence, the complement is a completer.

The student raised his hand.
The plants in the lobby are beautiful.

Some verbs in English never take a complement; they are known as intransitive verbs. (Mary smiled. Fred died.)

Some verbs always take a complement; they are known as transitive verbs. (Mary raised... what? The sentence will not make sense until we find out what noun completes the meaning begun by the subject and predicate.)

And some verbs can go either way. In a dictionary, you will see the designations tr. and intr. following a verb definition.

Going one step deeper, there are further subdivisions within the category of complements:

Direct Object - a noun complement following an action verb ("George carried the plants to the car.)
Predicate Nominative - a noun complement following a linking verb ("George is a marathoner.")
Predicate Adjective - an adjective complement following a linking verb ("George is tall.")

Modifiers

Pretty much everything else in a sentence beyond the subject, predicate, and complement, is a modifier of one kind or another. There are three basic kinds of modifying constructions:

single-word modifiers (adjectives and adverbs)
phrases (e.g. prepositional, participial, infinitive, and appositive)
clauses (a clause being defined as any group of words with its own subject and predicate)

Compound Elements

It should be noted that there may be more than one of any of these elements in a sentence. Compound elements can include:

Compound Subject: Mary and Tom went to the dance
Compound Predicate: He ran to the house and knocked at the door.
Compound Complement: I bought pencils and paper at the stationery store.
Compound Modifier: He was riding a black and white pony.