A clause is a group of words containing a subject and a predicate. There are two kinds of clauses: independent and dependent.

Independent clauses (also known as main clauses) can stand alone as complete sentences: The window is open. Pairs of independent clauses may be joined with a comma and a coordinating conjunction (and, but, for, or, nor, so, or yet).

The window is open, so we’d better be quiet.

Like independent clauses, dependent clauses (also known as subordinate clauses) contain a subject and a predicate, but they cannot stand alone as complete sentences because they begin with a subordinating word (31b). Dependent clauses function as nouns, adjectives, or adverbs.

Because the window is open, the room feels cool.

In this combination, the subordinating conjunction because transforms the independent clause the window is open into a dependent clause. In doing so, it indicates a causal relationship between the two clauses.