Clauses are the building blocks of sentences. A clause is a group of related words containing a subject and a verb. It can be simply distinguished from a phrase, which is a group of related words that does not contain a subject-verb relationship, such as "in the evening" or "walking down the street" or "having grown used to this ill treatment.” Like phrases, clauses are also classified as restrictive and nonrestrictive clauses. A nonrestrictive clause is not essential to the meaning of the sentence; it can be removed from the sentence without changing its basic meaning. 

There are two kinds of clauses: independent and dependent. Clauses are combined by three groups of words to form different kinds of sentences: coordinators, subordinators, conjunctive adverbs, and by means of a semicolon.