This document discusses clauses and their role as building blocks of sentences. It defines clauses as groups of words containing a subject and verb, and distinguishes them from phrases. There are two main types of clauses: independent clauses, which can stand alone as complete sentences, and dependent clauses, which cannot stand alone and must be attached to independent clauses. The document provides examples and definitions of different kinds of dependent clauses, including noun clauses, adverb clauses, adjective clauses, and relative clauses. It explains how understanding clauses can help avoid errors in sentence structure.