This document defines and provides examples of adjective phrases, adverb phrases, prepositional phrases, and clauses. It explains that adjective phrases have an adjective as the head and can include modifiers and qualifiers. Adverb phrases are structures with an adverb as the head, while adverbials are clause elements. Prepositional phrases are headed by a preposition and can take a complement. Clauses require a verb and are the key unit of syntax, with verbs determining the clause type as intransitive, monotransitive, copular, ditransitive, or complex transitive.