A clause is a group of words consisting of a subject (often just a single noun) and a predicate (sometimes just a single verb). A clause is either a whole sentence or, in effect a sentence-within-a-sentence.

Example:

• I didn't know that the dog ran through the yard.
  • through the yard is not a clause, but a phrase, since it has no subject or verb.
  • the dog ran through the yard is a clause; it is a whole sentence contained within a larger sentence.

Independent and dependent clauses

There are two basic categories of clauses: independent clauses and dependent clauses.

Independent clauses

The independent clause can stand by itself as a grammatically viable simple sentence. Multiple independent clauses can be joined (usually with a comma and a coordinating conjunction) to form a compound sentence.

Examples:

• I am a bus driver. (simple sentence)
• I want to be an astronaut. (simple sentence)
• I am a bus driver, but I want to be an astronaut. (compound sentence)
• Go to the store. (simple sentence) (Though a subject is not visible, in English the subject of an imperative is considered to be the pronoun 'you')

Dependent clauses

Dependent clauses (which are also sometimes referred to as subordinate clauses) cannot stand alone as sentences. They usually begin with subordinating conjunctions. A sentence with an independent clause and any number of dependent clauses is referred to as a complex sentence. One with two or more independent clauses and any number of dependent clauses is referred to as a compound-complex sentence.

Examples:

• My sister cried because she scraped her knee. (complex sentence)
  • Subjects: My sister, she
  • Predicates: cried, scraped her knee
  • Subordinating conjunction: because

• When they told me I won the contest, I cried, but I didn't faint. **(compound-complex sentence)
  • Subjects: they, I, I, I
  • Predicates: told me, won the contest, cried, didn't faint
  • Subordinating conjunctions: When, that (understood)
  • Coordinating conjunction: but

The above sentence actually contains two dependent clauses. "When they told me" is one; the other is "(that) I won the contest." The "that" is understood to precede the "I won" and functions as a subordinating conjunction.

Types of dependent clauses

There are a few types of dependent clauses, each of which functions as a part of speech: noun clauses, adjective clauses, and adverb clauses.

Examples:

• That the kid was making so much money bothered me.
  • Noun clause: That the kid was making so much money (functions as a subject)

• Her eyes were a shade of blue that reminded me of the sea.
  • Adjective clause: that reminded me of the sea

• I have a tendency to hyperventilate when I'm upset.
  • Adverb clause: when I'm upset

Clauses should not be confused with phrases, which do not express complete thoughts through combinations of subjects and predicates. Phrases generally do not contain verbs except as verbals (gerunds, participles, and infinitives).