In linguistics, head directionality is a proposed parameter that classifies languages according to whether they are head-initial (the head of a phrase precedes its complements) or head-final (the head follows its complements). The head is the element that determines the category of a phrase: for example, in a verb phrase, the head is a verb. Therefore, head initial would be "VO" languages and head final would be "OV" languages.
Some languages are consistently head-initial or head-final at all phrasal levels. English is considered to be mainly head-initial (verbs precede their objects, for example), while Japanese is an example of a language that is consistently head-final. In certain other languages, such as German and Gbe, examples of both types of head directionality occur. Various theories have been proposed to explain such variation.
Head directionality is connected with the type of branching that predominates in a language: head-initial structures are right-branching, while head-final structures are left-branching. On the basis of these criteria, languages can be divided into head-final (rigid and non-rigid) and head-initial types. The identification of headedness is based on the following: the order of subject, object, and verb the relationship between the order of the object and verb the order of an adposition and its complement the order of relative clause and head noun.
Types of phrase In some cases, particularly with noun and adjective phrases, it is not always clear which dependents are to be classed as complements, and which as adjuncts. Although in principle the head-directionality parameter concerns the order of heads and complements only, considerations of head-initiality and head-finality sometimes take account of the position of the head in the phrase as a whole, including adjuncts. The structure of the various types of phrase is analyzed below in relation to specific languages, with a focus on the ordering of head and complement. In some cases (such as English and Japanese) this ordering is found to be the same in practically all types of phrase, whereas in others (such as German and Gbe) the pattern is less consistent. Different theoretical explanations of these inconsistencies are discussed later in the article. There are various types of phrase in which the ordering of head and complement(s) may be considered when attempting to determine the head directionality of a language, including:
Verb Phrase: the head of verb phrase (VP) is a verb, and the complement(s) are most commonly objects of various types. The ordering here is related to one of the chief questions in the word order typology of languages, namely the normal order of subject, verb and object within a clause (languages are classed on this basis as SVO, SOV, VSO, etc.).
Noun Phrase: the head of a noun phrase (NP) is a noun; various kinds of complementizer phrases (CPs) and adpositional phrases (PPs) can be complements.
Adjective Phrase: the head of an adjective phrase (AP) is an adjective, which can take as a complement, for example, an adverbial phrase or adpositional phrase (PP).
Adpositional Phrase: the head of an adpositional phrase (PP) is an adposition. Such phrases are called prepositional phrases if they are head-initial (i.e. headed by a preposition), or postpositional phrases if they are head-final (i.e. headed by a postposition). The complement is a determiner phrase (or noun phrase, depending on analytical scheme followed).
Determiner Phrase: the head of a determiner phrase (DP) is a determiner. DPs were proposed under generative syntax; not all theories of syntax agree that they exist. Complementizer Phrase: the head of a complementizer phrase (CP) is a complementizer, like that in English. In some cases the C head is covert (not overtly present). The complement of C is generally agreed to be a tense phrase (TP).
Tense Phrase: the head of a tense phrase (TP) is tense; these are phrases in which the head is an abstract category representing tense; the complement is a verb phrase. Aspect Phrase: the head of an aspect phrase (AspP) is aspect; these are phrases in which the head is an abstract syntactic category representing aspect. In more traditional analysis the entire phrase (including any elements denoting tense or aspect) is considered to be simply a verb phrase.
Head-initial languages
English English is a mainly head-initial language. In a typical verb phrase, for example, the verb precedes its complements, as in the following example:
eat an apple [VP [V eat] [DP an apple]]
The head of the phrase (the verb eat) precedes its complement (the determiner phrase an apple). Switching the order to "[VP [DP an apple] [V eat]]" would be ungrammatical.
Nouns also tend to precede any complements, as in the following example, where the relative clause (or complementizer phrase) that follows the noun may be considered to be a complement:
He married a girl who is from Texas. [NP [N girl] [CP who is from Texas]]
Nouns do not necessarily begin their phrase; they may be preceded by attributive adjectives, but these are regarded as adjuncts rather than complements. Adjectives themselves may be preceded by adjuncts, namely adverbs, as in extremely happy. However, when an adjective phrase contains a true complement, such as a prepositional phrase, the head adjective precedes it: a person happy about her work [AP [A happy] [PP about her work]]
English adpositional phrases are also head-initial; that is, English has prepositions rather than postpositions:
a majority of eligible voters [PP [P of] [DP eligible voters]]
On the determiner phrase (DP) view, where a determiner is taken to be the head of its phrase (rather than the associated noun), English can be seen to be head-initial in this type of phrase too. In the following example the head is taken to be the determiner any, and the complement is the noun (phrase) book:
any book [DP [D any] [NP book]]
English also has head-initial complementizer phrases, as in this example where the complementizer that precedes its complement, the tense phrase Mary did not swim: We saw that Mary did not swim [CP [C that] [TP Mary did not swim]]
Grammatical words marking tense and aspect generally precede the semantic verb. This indicates that, if finite verb phrases are analyzed as tense phrases or aspect phrases, these are again head-initial in English. In the example above, did is considered a (past) tense marker, and precedes its complement, the verb phrase not swim. In the following, has is a (perfect) aspect marker; again it appears before the verb (phrase) which is its complement.
John has arrived [AspP [Asp has] [VP arrived]]
The following example shows a sequence of nested phrases in which each head precedes its complement. In the complementizer phrase (CP) in (a), the complementizer (C) precedes its tense phrase (TP) complement. In the tense phrase in (b), the tense-marking element (T) precedes its verb phrase (VP) complement. (The subject of the tense phrase, the girl, is a specifier, which does not need to be considered when analyzing the ordering of head and complement.) In the verb phrase in (c), the verb (V) precedes its two complements, namely the determiner phrase (DP) the book and the prepositional phrase (PP) on the table. In (d), where a picture is analyzed as a determiner phrase, the determiner (D) a precedes its noun phrase (NP) complement, while in (e), the preposition (P) on precedes its DP complement your desk. You know that the girl will put a picture on your desk. a. CP: [CP [C that ] [TP the girl will put a picture on your desk ] ] b. TP: [TP [T will ] [VP put a picture on your desk ] ] c. VP: [VP [V put ] [DP a picture ] [PP on your desk ] ] d. DP: [DP [D a ] [NP picture ] ] e. PP: [PP [P on ] [DP your desk ] ]
Indonesian Indonesian is an example of an SVO head-initial language. The characteristic of it being a head-initial language can be examined through a dependency perspective or through a word order perspective. Both approaches lead to the conclusion that Indonesian is a head-initial language.
Dependency perspective
When examining Indonesian through a dependency perspective, it is considered head initial as the governor of both constituents are positioned before the dependent.
Placing the head before a dependent minimizes the overall dependency distance, which is the distance between the two constituents. Minimizing dependency distance allows for less cognitive demand as a head-final dependency requires the constituents in the dependent clause to be stored in working memory until the head is realized.
In Indonesian, the number of constituencies affects the dependency direction. When there are 6 constituents — which is a relatively short sentence — there is a preference for head initial relation. However, when there are 11-30 constituents, there appears to be a balance of head-initial and head-final dependencies. Regardless, Indonesian displays an overall head-initial preference on all levels of dependency structure as it consistently attempts to position the head as early on in the sentence even though it produces a longer dependency distance rather than placing the head after its dependents. Furthermore, Indonesian has an overall preference towards head-initial when comparing head-initial and head-final relation on all levels of constituent length for both spoken and written data.
Word order perspective The subject of the sentence followed by the verb, representing SVO order. The following examples demonstrate head-initial directionality in Indonesian (note that "prime minister" is unusually being head-final):
[CP [DP ] [VP ]]
Classifiers and partitives can function as the head nouns of noun phrases. Below is an example of the internal structure of a noun phrase and its head-initial word order.
[CP[DP ][VP ]]
Head-initial word order is seen in the internal structure of the verb phrase in the following example where the V is in the head position of the verb phrase and thus appears before its complement:
[CP[DP][VP[V ][DP]]]
In Indonesian a noun can be followed by another modifying noun whose primary function is to provide more specific information about the preceding head noun, such as indicating what the head noun is made of, gender, locative sense, and what the head noun does, etc. However, no other word is able to intervene between a head noun and its following modifying noun. If a word follows the modifying noun, then it provides reference to the head noun and not the modifying noun. Head noun: [N ] + Modifying noun: [N ]
Head noun: [N ] + Modifying noun: [N ] + Determiner [D ]
Head noun: [N] + Modifying noun: [N ]
Head noun: [N] + Modifying noun: [N ] + Determiner phrase [DP]
Head noun: [N ] + Modifying noun: [N ]
Head-final languages
Japanese Japanese is an example of a strongly head-final language. This can be seen in verb phrases and tense phrases: the verb ( in the example) comes after its complement, while the tense marker () comes after the whole verb phrase which is its complement.
[TP [VP [DP ] [V ]] [T ]]
Nouns also typically come after any complements, as in the following example where the PP may be regarded as a complement:
[NP [PP ] [N ]]
Adjectives also follow any complements they may have. In this example the complement of quantity, ("twenty meters"), precedes the head adjective ("tall"):
[AP [Q ] [A ]]
Japanese uses postpositions rather than prepositions, so its adpositional phrases are again head-final:
[PP [DP ] [P ]]
Determiner phrases are head-final as well:
[DP [NP ] [D ]]
A complementizer (here , equivalent to English "that") comes after its complement (here a tense phrase meaning "Mary did not swim"), thus Japanese complementizer phrases are head-final:
[CP [TP ] [C ]]
Turkish