A simple sentence includes a single independent clause made up of a subject and a predicate. The subject and the predicate may each be a single word or a group of words. In addition to its verb, the predicate may include objects, complements, and adverbial modifiers.

Simple sentences, then, are composed of some combination of these basic units:

Subject (S) The simplest subject can be a single noun or pronoun, but a subject may also consist of a noun phrase (including adjectives and other sentence elements) or even a noun clause. Subjects may also be compound when two or more nouns or pronouns are linked by a conjunction. (See R2 for definitions and examples of these various elements.)

Verb (V) These can be classified as transitive, when they occur with an object, or intransitive, when they occur without an object. Intransitive verbs that occur with complements are often called linking verbs. Like subjects, verbs may be compound.

Objects (DO, IO) These include direct objects (DO) and indirect objects (IO), which, like subjects, can be nouns, noun phrases, noun clauses, or pronouns. Objects usually follow the subject and verb.

Complements (SC, OC) These are either subject complements or object complements: Subject complements (SO) refer to the subject, object complements (OC) to an object. Like subjects and objects, complements can be nouns or pronouns, noun phrases, or noun clauses (sometimes referred to as predicate nominatives). Complements can also be adjectives or adjective phrases (sometimes called predicate adjectives). Like objects, complements usually follow the subject and verb. They also follow any objects.

Adverbial (A) These are modifiers that refer to the verb in the sentence. They can be adverbs, adverb phrases, or adverb clauses.

Of these seven units, two—subject and verb—are required in every sentence.