Phrases and clauses are the building blocks of sentences. Phrases are groups of words that act as a part of speech but cannot stand alone as a sentence. The words in a phrase act together so that the phrase itself functions as a single part of speech. For example, phrases can function as nouns, verbs, adjectives, or adverbs. If you understand how different types of phrases function, you can avoid misplacing them or leaving them dangling in sentences.
Clauses are groups of words that have a subject and a predicate. Independent clauses express a complete thought and can stand alone as a sentence. Subordinate clauses can act as parts of speech but depend on the rest of the sentence to express a complete thought.
A sentence expresses a complete thought and contains a subject (a noun or pronoun) and a predicate (a verb or verb phrase). The four basic types of sentences—simple, compound, complex, and compound‐complex—use phrases and clauses in varying degrees of complexity.