syntax

Syntax is the set of rules that governs the structure of sentences in natural languages and the arrangement of symbols in formal languages. In linguistics, syntax specifies how words combine into phrases and clauses to form well-formed sentences, and it is distinct from semantics (meaning) and morphology (word formation). Key ideas include syntactic categories such as nouns, verbs, and adjectives, functional categories like noun phrases and verb phrases, and the hierarchical organization of phrases into trees that reflect grammatical relationships.

In linguistic theory, syntax examines how different languages arrange elements for conveying information, the rules that allow or constrain word order, and how movement or agreement processes produce variations without altering core meaning. Topics include phrase structure, constituency, and the distinction between surface structure and deeper representations, with debates about universals and parameters in cross-linguistic grammar. The field has been significantly influenced by generative approaches that treat syntax as a rule-governed system capable of generating a vast range of sentences from a finite set of principles.

In formal and computational contexts, syntax defines the allowable sequences of symbols in programming languages and data formats. Grammars such as context-free grammars specify productions that build strings from terminals and nonterminals. Notation like Backus–Naur Form (BNF) or extended BNF expresses these rules, and parsers construct syntax trees to check correctness and guide subsequent processing. Syntax errors, such as mismatched parentheses or missing semicolons, prevent programs from executing and are a primary focus of compilers and interpreters.