Depending on the number and the types of clauses they contain, sentences are classified as simple, compound, complex, or compound-complex.

Clauses come in two varieties: independent and subordinate. An independent clause contains a subject and a predicate, and it either stands alone or could stand alone as a sentence. A subordinate clause also contains a subject and a predicate, but it functions within a sentence as an adjective, an adverb, or a noun; it cannot stand alone. (See 48e.)

Simple sentences

A simple sentence is one independent clause with no subordinate clauses.

A simple sentence may contain compound elements—a compound subject, verb, or object, for example—but it does not contain more than one full sentence pattern. The following sentence is simple because its two verbs (comes in and goes out) share a subject (Spring).

Compound sentences

A compound sentence is composed of two or more independent clauses with no subordinate clauses. The independent clauses are usually joined with a comma and a coordinating conjunction (and, but, or, nor, for, so, yet) or with a semicolon. (See 14a.)

Complex sentences

A complex sentence is composed of one independent clause with one or more subordinate clauses. (See 48e.)

Compound-complex sentences

A compound-complex sentence contains at least two independent clauses and at least one subordinate clause. The following sentence contains two independent clauses, each of which contains a subordinate clause.