In linguistics, syntax (/ˈsɪntæks/) is the set of rules, principles, and processes that govern the structure of sentences (sentence structure) in a given language, usually including word order. The term syntax is also used to refer to the study of such principles and processes. The goal of many syntacticians is to discover the syntactic rules common to all languages. In linguistics, syntax (/ˈsɪntæks/) is the set of rules, principles, and processes that govern the structure of sentences (sentence structure) in a given language, usually including word order. The term syntax is also used to refer to the study of such principles and processes. The goal of many syntacticians is to discover the syntactic rules common to all languages. In mathematics, syntax refers to the rules governing the notation of mathematical systems, such as formal languages used in logic. The word syntax comes from Ancient Greek: σύνταξις 'coordination', which consists of σύν syn, 'together', and τάξις táxis, 'an ordering'. One basic description of a language's syntax is the sequence in which the subject (S), verb (V), and object (O) usually appear in sentences. Over 85% of languages usually place the subject first, either in the sequence SVO or the sequence SOV. The other possible sequences are VSO, VOS, OVS, and OSV, the last three of which are rare. In most generative theories of syntax, these surface differences arise from a more complex clausal phrase structure, and each order may be compatible with multiple derivations. The Aṣṭādhyāyī of Pāṇini (c. 4th century BC in Ancient India), is often cited as an example of a premodern work that approaches the sophistication of a modern syntactic theory (as works on grammar were written long before modern syntax came about). In the West, the school of thought that came to be known as 'traditional grammar' began with the work of Dionysius Thrax. For centuries, a framework known as grammaire générale (first expounded in 1660 by Antoine Arnauld in a book of the same title) dominated work in syntax: as its basic premise the assumption that language is a direct reflection of thought processes and therefore there is a single, most natural way to express a thought. However, in the 19th century, with the development of historical-comparative linguistics, linguists began to realize the sheer diversity of human language and to question fundamental assumptions about the relationship between language and logic. It became apparent that there was no such thing as the most natural way to express a thought, and therefore logic could no longer be relied upon as a basis for studying the structure of language. The Port-Royal grammar modeled the study of syntax upon that of logic. (Indeed, large parts of the Port-Royal Logic were copied or adapted from the Grammaire générale.) Syntactic categories were identified with logical ones, and all sentences were analyzed in terms of 'subject – copula – predicate'. Initially, this view was adopted even by the early comparative linguists such as Franz Bopp. The central role of syntax within theoretical linguistics became clear only in the 20th century, which could reasonably be called the 'century of syntactic theory' as far as linguistics is concerned. (For a detailed and critical survey of the history of syntax in the last two centuries, see the monumental work by Giorgio Graffi (2001).)