In linguistics, branching is the general tendency towards a given order of words within sentences and smaller grammatical units within sentences (such as subordinate propositions, prepositional phrases, etc.). Such ordering and nesting of phrases can be represented as a tree where branches can be divided into other minor branches, which may also branch in turn.
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Language typically construct phrases with a head word (or nucleus) and zero or more dependents (modifiers). For example, in English a noun phrase can be constructed as follows:
In a dependent clause, the head word is the verb, and the dependents are the arguments of the verb. In a noun phrase, the head word is the main noun, and the dependents are the adjective, the numeral, the genitive (-'s) of noun, and the relative clause.
There are also verb phrases, prepositional phrases, and the like. In every case, the constituents are placed in a given order, which is more or less fixed according to the language in question. Also in some cases, the dependents can in turn be the head words of inner phrases (as in "the black cat's paws", "an awfully messy room", etc.).
Branching is typically ordered. In English, an article can be added to a bare noun only by placing it before the noun. An adjective can usually be added to an article-noun phrase only in between the article and the noun, whereas a dependent clause can be added only following the noun. This is also true of prepositional phrases. The subject comes before the main verb in the vast majority of sentences in the indicative mood, and the direct object in a sentence is nearly always found following its main verb.
The rules exemplified above constitute the branching tendency of the language, which can be predominantly left-branching or right-branching.
Left-branching languages, such as Turkish, Japanese, Tamil, and Basque tend to place dependents before the head words. Adjectives precede nouns, direct objects come before verbs, and there are postpositions. In less formal terminology, this ordering is called head-last or head-final.
An example from Basque:
Right-branching languages, such as Spanish, Arabic, and Khmer tend to place dependents after the head words. Adjectives follow nouns, direct objects follow verbs, and adpositions are prepositional. This is also known as head-first order.
An example from the Spanish:
Reenumerating the sentence to compare against the English word order:
we can see the similarity between these two right-branching languages:
with the only distinction being adjective placement.
Though articles (words like a and the in English) have been thought of as the dependents of nouns, it is now thought that articles and nouns form a dependent phrase, in which the article is the head.[2] Consistent with this new view, languages that place the verb before the object in clauses also tend to place the article before the noun, and languages that place the verb after the object also tend to place the article after the noun.[3]
For most languages, the main branching tendency is just a tendency and it often shows exceptions. Spanish, for example, while overwhelmingly right-branching, puts numeral modifiers before nouns and, in certain cases, objects before verbs. Languages like English and German - though regarded as being right-branching because the main verbs precede direct objects - place adjectives and numerals before their nouns. Japanese and most other languages of northeastern Asia and the Indian subcontinent, on the other hand, are practically a model for rigidly left-branching languages. The Mon–Khmer and Austronesian languages of southeast Asia and many African languages come close to rigidly right-branching, with numerals as well as adjectives following their nouns and degree words like "very", "too", "extremely", "quite" following the adjectives they modify.