What is the study of the structure of sentences called?

The study of the structure of sentences is called syntax.

Syntax is the branch of linguistics that examines how words and morphemes combine into phrases, clauses, and sentences. It studies patterns such as word order, grammatical relationships, agreement, and the hierarchical organization of sentence parts. In English, “The cat chased the mouse” follows a different structural pattern from “The mouse chased the cat,” even though both sentences contain the same basic nouns and verb.

Languages organize sentences in different ways. English usually follows subject–verb–object order, while languages such as Japanese commonly place the object before the verb. Syntax explains how speakers recognize these patterns and understand which combinations sound grammatical in a particular language.

Syntax is related to, but distinct from, nearby linguistic fields. Morphology studies the internal structure of words; phonology studies sound systems; and semantics studies meaning. A sentence can have well-formed syntax but unusual or nonsensical meaning. Noam Chomsky’s 1957 book “Syntactic Structures” helped make formal theories of sentence structure especially influential in modern linguistics.