Dependency grammar (DG) is a class of modern syntactic theories that are all based on the dependency relation (as opposed to the constituency relation) and that can be traced back primarily to the work of Lucien Tesnière. Dependency is the notion that linguistic units, e.g. words, are connected to each other by directed links. The (finite) verb is taken to be the structural center of clause structure. All other syntactic units (words) are either directly or indirectly connected to the verb in terms of the directed links, which are called dependencies. DGs are distinct from phrase structure grammars (constituency grammars) since DGs lack phrasal nodes although they acknowledge phrases. Structure is determined by the relation between a word (a head) and its dependents. Dependency structures are flatter than constituency structures in part because they lack a finite verb phrase constituent, and they are thus well suited for the analysis of languages with free word order, such as Czech, Turkish, and Warlpiri.
The notion of dependencies between grammatical units has existed since the earliest recorded grammars, e.g. Pāṇini, and the dependency concept therefore arguably predates the constituency notion by many centuries.Ibn Maḍāʾ, a 12th-century linguist from Córdoba, Andalusia, may have been the first grammarian to use the term dependency in the grammatical sense that we use it today. In early modern times, the dependency concept seems to have coexisted side by side with the constituency concept, the latter having entered Latin, French, English and other grammars from the widespread study of term logic of antiquity. Dependency is also concretely present in the works of Sámuel Brassai (1800–1897), a Hungarian linguist, and of Heimann Hariton Tiktin (1850–1936), a Romanian linguist.