|Applied and experimental|
In linguistics, the 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.)
Some languages are consistently head-initial or head-final at all phrasal levels. English is considered to be strongly head-initial, 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 direction 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.
Types of phrase
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 (VP). Here the head 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 (NP). Here the head is a noun; various kinds of complementizer phrase and adpositional phrase may be considered to be complements.
- Adjective phrase (AP). This contains an adjective as the head, and can take as a complement, for example, an adverbial phrase or adpositional phrase.
- Adpositional phrase (PP). 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). For more on these, see Preposition and postposition. The complement is a determiner phrase (or noun phrase, depending on analytical scheme followed).
- Determiner phrase (DP). This has a determiner as the head of the phrase. DPs were proposed under generative syntax; not all theories of syntax agree that they exist.
- Complementizer phrase (CP). This contains a complementizer, like that in English, as the head. In some cases the head is covert (not overtly present). The complement can be considered to be a tense phrase.
- Tense phrase (TP) and aspect phrase (AspP). These are phrases in which the head is an abstract category representing tense or aspect; the complement is a verb phrase. In more traditional analysis the entire phrase (including any elements denoting tense or aspect) is considered to be simply a verb 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.
- 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.
- 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. (For preceding determiners, see below.) 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]]
- 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]]
- 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 ] ]
German, while being predominantly head-initial, is less conclusively so than in the case of English. German also features certain head-final structures. For example, in a nonfinite verb phrase the verb is final. In a finite verb phrase (or tense/aspect phrase) the verb (tense/aspect) is initial, although it may move to final position in a subordinate clause. In the following example, the verb phrase es finden is head-final, whereas the tense phrase werde es finden (headed by the auxiliary verb werde indicating future tense) is head-initial.
- Ich werde es finden
- I will it find
- "I will find it."
- [TP [T werde] [VP [DP es] [V finden]]]
Noun phrases containing complements are head-initial; in this example the complement, the CP der den Befehl überbrachte, follows the head noun Boten.
- Man beschimpfte den Boten, der den Befehl überbrachte
- one insulted the messenger who the command delivered
- "The messenger who delivered the command was insulted."
- [NP [N Boten] [CP der den Befehl überbrachte]]
Adjective phrases may be head-final or head-initial. In the next example the adjective (stolze) follows its complement (auf seine Kinder).
- der auf seine Kinder stolze vater
- the of his children proud father
- "the father (who is) proud of his children"
- [AP [PP auf seine Kinder] [A stolze]]
- weil er stolz auf seine Kinder ist
- since he proud of his children is
- "since he is proud of his children"
- [AP [A stolz] [PP auf seine Kinder]]
Most adpositional phrases are head-initial (as German has mostly prepositions rather than postpositions), as in the following example, where auf comes before its complement den Tisch:
- Peter legt das Buch auf den Tisch
- Peter puts the book on the.ACC table
- "Peter puts the book on the table."
- [PP [P auf] [DP den Tisch]]
German also has some postpositions, however (such as gegenüber "opposite"), and so adpositional phrases can also sometimes be head-final. Another example is provided by the analysis of the following sentence:
- Die Schnecke kroch das Dach hinauf
- the snail crept the roof up
- "The snail crept up the roof"
- [PP [DP das Dach] [P hinauf]]
Like in English, determiner phrases and complementizer phrases in German are head-initial. The next example is of a determiner phrase, headed by the article der:
- der Mann
- the man
- "the man"
- [DP [D der] [NP Mann]]
In the following example, the complementizer daß precedes the tense phrase which serves as its complement:
- daß Lisa eine Blume gepflanzt hat
- that Lisa a flower planted has
- "that Lisa planted a flower"
- [CP [C daß] [TP Lisa eine Blume gepflanzt hat]]
Japanese is an example of a strongly head-final language. This can be seen in verb phrases and tense phrases: the verb (tabe in the example) comes after its complement, while the tense marker (ru) comes after the whole verb phrase which is its complement.
- ringo-o tabe-ru
- apple-ACC eat-NONPAST
- "eat an apple"
- [TP [VP [DP ringo-o] [V tabe]] [T ru]]
Nouns also typically come after any complements, as in the following example where the PP New York-de-no may be regarded as a complement:
- John-no kinoo-no New York-de-no koogi
- John-GEN yesterday-GEN New York-in-GEN lecture
- "John's lecture in New York yesterday"
- [NP [PP New York-de-no] [N koogi]]
Adjectives also follow any complements they may have. In this example the complement of quantity, ni-juu-meetoro ("twenty meters"), precedes the head adjective takai ("tall"):
- Kono biru-wa ni-juu-meetoru takai
- this building-TOPIC two-ten-meter tall
- "This building is twenty meters taller."
- [AP [Q ni-juu-meetoru] [A takai]]
Japanese uses postpositions rather than prepositions, so its adpositional phrases are again head-final:
- Boku-ga Takasu-mura-ni sunde-iru
- I-NOM Takasu-village-in live-PRES
- "I live in Takasu village."
- [PP [DP Takasu-mura] [P ni]]
Determiner phrases are head-final as well:
- dare mo
- person any
- [DP [NP dare] [D mo]]
A complementizer (here to, equivalent to English "that") comes after its complement (here a tense phrase meaning "Mary did not swim"), thus Japanese complementizer phrases are head-final:
- Mary-ga oyog-ana-katta-to
- Mary-NOM swim-NEG-PAST-that
- "that Mary did not swim"
- [CP [TP Mary-ga oyog-ana-katta] [C to]]
Standard Chinese (whose syntax is typical of Chinese languages generally) features a mixture of head-final and head-initial structures. Noun phrases are head-final – modifiers virtually always precede the noun they modify. For examples of this involving relative clauses, see Relative clause → Mandarin.
In the case of strict head/complement ordering, however, Chinese appears to be head-initial. Verbs normally precede their objects. Both prepositions and postpositions are reported, but the postpositions can be analyzed as a type of noun (the prepositions are often called coverbs). For more details and examples of the relevant structures, see Chinese grammar. For a head-direction analysis of Chinese aspect phrases, see the theoretical section below.
In Gbe, a mixture of head-initial and head-final structures is found. For example, a verb may appear after or before its complement, which means that both head-initial and head-final verb phrases occur. In the first example the verb for "use" appears after its complement:
- Kɔ̀jó tó àmí lɔ́ zân
- Kojo IMPERF oil DET use
- "Kojo is using the oil."
- [VP [DP àmí lɔ́] [V zân]]
In the second example the verb precedes the complement:
- Kɔ̀jó nɔ̀ zán àmí lɔ́
- Kojo HAB use-PERF oil DET
- "Kojo habitually used the oil/Kojo habitually uses the oil."
- [VP [V zán] [DP àmí lɔ́]]
It has been debated whether the first example is due to object movement to the left side of the verb  or whether the lexical entry of the verb simply allows head-initial and head-final structures.
Tense phrases and aspect phrases are head-initial, since aspect markers (such as tó and nɔ̀ above) and tense markers (such as the future marker ná in the following example, although this does not apply to tense markers shown by verb inflection) come before the verb phrase.
- dàwé lɔ̀ ná xɔ̀ kɛ̀kɛ́
- man DET FUT buy bicycle
- "The man will buy a bicycle."
- [TP [T ná] [VP xɔ̀ kɛ̀kɛ́]]
Gbe noun phrases are typically head-final, as in this example:
- Kɔ̀kú sín ɖìdè lɛ̀
- Koku-CASE sketch-PL
- "sketches of Koku"
- [NP [KP Kɔ̀kú sín] [N ɖìdè]]
- àǔn yù tàùú
- dog black-Int
- "really black dogs"
- [AP [A yù] [Int tàùú]]
Gbe adpositional phrases are head-initial, with prepositions preceding their complement:
- Kòfi zé kwɛ́ xlán Àsíbá"
- Kofi take-PERF money to Asiba
- "Kofi sent money to Asiba."
- [PP [P xlán] [DP Àsíbá]]
Determiner phrases, however, are head-final:
- Asíbá xɔ̀ àvɔ̀ àmàmú màtàn-màtàn ɖé
- Asiba buy-PERF cloth green odd DEF
- "Asiba bought a specific ugly green cloth"
- [DP [NP àvɔ̀ àmàmú màtàn-màtàn] [D ɖé]]
Complementizer phrases are head-initial:
- ɖé Dòsà gbá xwé ɔ̀ ɔ̀
- that Dosa build-PERF house DEF DET
- "that Dosa built the house"
- [CP [C ɖé] [TP Dòsà gb xwé ɔ̀ ɔ̀]]
The idea that syntactic structures reduce to binary relations was introduced by Lucien Tesnière within the framework of dependency theory, which was developed during the 1960s. Tesnière distinguished two structures that differ in the placement of the structurally governing element (head): centripetal structures, in which heads precede their dependents, and centrifugal structures, in which heads follow their dependents. Dependents here may include complements, adjuncts, and specifiers.
- If a language has VO (verb-before-object) ordering, then it will also have prepositions (rather than postpositions), and genitives and adjectives will be placed after the noun they modify.
- If a language has OV ordering, then it will also have postpositions, and genitives and adjectives will be placed before the noun they modify.
The first set of properties make heads come at the start of their phrases, while the second set make heads come at the end. However, it has been claimed that many languages (such as Basque) do not fulfill the above conditions, and that Greenberg's theory fails to predict the exceptions.
Noam Chomsky's Principles and Parameters theory in the 1980s introduced the idea that a small number of innate principles are common to every human language (e.g. phrases are oriented around heads), and that these general principles are subject to parametric variation (e.g. the order of heads and other phrasal components may differ). In this theory, the dependency relation between heads, complements, specifiers, and adjuncts is regulated by X-bar theory, proposed by Jackendoff in the 1970s. The complement is sister to the head, and they can be ordered in one of two ways. A head-complement order is called a head-initial structure, while a complement-head order is called a head-final structure. These are special cases of Tesnière's centripetal and centrifugal structures, since here only complements are considered, whereas Tesnière considered all types of dependents.
In the principles and parameters theory, a head-directionality parameter is proposed as a way of classifying languages. A language which has head-initial structures is considered to be a head-initial language, and one which has head-final structures is considered to be a head-final language. It is found, however, that very few, if any, languages are entirely one direction or the other. Linguists have come up with a number of theories to explain the inconsistencies, sometimes positing a more consistent underlying order, with the phenomenon of phrasal movement being used to explain the surface deviations.
According to the Antisymmetry Theory proposed by Richard Kayne, there is no head-directionality parameter as such: it is claimed that at an underlying level, all languages are head-initial. In fact, it is argued that all languages have the underlying order Specifier-Head-Complement. Deviations from this order are accounted for by different syntactic movements applied by languages.
Kayne argues that a theory that allows both directionalities would imply an absence of asymmetries between languages, whereas in fact languages are found not to be symmetrical in many respects. Some examples of linguistic asymmetries which may be cited in support of the theory (although they do not concern head direction) are listed below.
- Hanging topics appear at the start of sentences, as in "Henry – I've known that guy for a long time". They are not attested at the end of sentences.
- Number agreement is stronger when the noun phrase precedes the verb (Greenberg's Universal 33). Examples of this are found in English sentences such as There's books on the table, where the verb frequently fails to agree with the following plural noun, and in French and Italian compound tenses, where the past participle may agree with a preceding direct object but not with a following one.
- Relative clauses which precede the noun (as in Chinese and Japanese) tend to differ from those that follow the noun: they more often lack complementizers (akin to English that) or relative pronouns, and are more likely to be non-finite (this can be found, for example, in Quecha).
- Other areas in which asymmetries are found, according to Kayne, include clitics and clitic dislocation, serial verb constructions, coordination, and forward and backward pronominalization.
In arguing for a universal underlying Head-Complement order, Kayne uses the concept of a probe-goal search (based on the Minimalist program). The idea of probes and goals in syntax is that a head acts as a probe and looks for a goal, namely its complement. Kayne proposes that the direction of the probe-goal search must share the direction of language parsing and production. Parsing and production proceed in a left-to-right direction: the beginning of sentence is heard or spoken first, and the end of the sentence is heard or spoken last. This implies (according to the theory) an ordering whereby probe comes before goal, i.e. head precedes complement.
- S H [c...
The specifier, at first internal to the complement, is moved to the unoccupied position to the left of the head. In terms of merged pairs, this structure can also be represented as:
- <S, H> <H, C>
This process can be mapped onto X-bar syntactic trees as shown in the diagram to the right.
Antisymmetry, then, leads to a universal Specifier-Head-Complement order. The many cases of different ordering found in various languages would have to be explained by syntactic movement away from this underlying base order. It has been pointed out, though, that in predominantly head-final languages such as Japanese and Basque, this would involve complex and massive leftward movement, which is not in accordance with the ideal of grammatical simplicity. An example of the type of movement scheme that would need to be envisaged is provided by Tokizaki:
a. [CP C [IP ... [VP V [PP P [NP N [Genitive Affix Stem]]]]]] b. [CP C [IP ... [VP V [PP P [NP N [Genitive Stem Affix]]]]]] c. [CP C [IP ... [VP V [PP P [NP [Genitive Stem Affix] N]]]]] d. [CP C [IP ... [VP V [PP [NP [Genitive Stem Affix] N] P]]]] e. [CP C [IP ... [VP [PP [NP [Genitive Stem Affix] N] P] V]]] f. [CP [IP ... [VP [PP [NP [Genitive Stem Affix] N] P] V]] C]
Here, at each phrasal level in turn, the head of the phrase moves from left to right position relative to its complement. The eventual result reflects the ordering of complex nested phrases found in a language like Japanese.
An attempt to provide evidence for Kayne's scheme is made by Lin, who considered Standard Chinese sentences with the sentence-final particle le. This particle is taken to convey perfect aspectual meaning, and thus to be the head of an aspect phrase, having the verb phrase as its complement. If phrases are always to be underlyingly head-initial, then a case like this must entail movement, since the particle comes after the verb phrase. It is proposed that here the complement moves into specifier position, which precedes the head.
As evidence for this, Lin considers (among others) wh-adverbials such as zenmeyang ("how?"). Based on prior work by Huang, it is postulated that (a) adverbials of this type are subject to movement at Logical Form (LF) level (even though, in Chinese, they do not display wh-movement at surface level); and (b) movement is not possible from within a non-complement (Huang's Condition on Extraction Domain or CED). This would imply that zenmeyang could not appear in a verb phrase with sentence-final le, assuming the above analysis, since that verb phrase has moved into a non-complement (specifier) position, and thus further movement (such as that which zenmeyang is required to undergo at LF level) is not possible. Such a restriction on the occurrence of zenmeyang is indeed found:
(a) Zhangsan zenmeyang xiu che? Zhangsan how repair car "How does Zhangsan repair the car?" (b) *Zhangsan zenmeyang xiu che le? Zhangsan how repair car PF ("How has Zhangsan repaired the car?")
Sentence (b), in which zenmeyang co-occurs with sentence-final le, is found to be ungrammatical. Lin cites this and other related findings as evidence that the above analysis is correct, supporting the view that Chinese aspect phrases are deeply head-initial.
Surface true approach
According to the "surface true" viewpoint, analysis of head direction must take place at the level of surface derivations, or even the Phonetic Form (PF), i.e. the order in which sentences are pronounced in natural speech. This rejects the idea of an underlying ordering which is then subject to movement, as posited in the Antisymmetry Theory (described above) and in certain other approaches. In a 2008 article, the linguist Marc Richards argued that a head parameter must only reside at PF, as it is unmaintainable in its original form as a structural parameter. In this approach the relative positions of head and complement that are actually attested at this surface level, which are found to show variation both between and within languages (see above), must be treated as the "true" orderings.
Existence of true head-final languages
Takita (2009) argues against the conclusion of Kayne's Antisymmetry Theory which states that all languages are head-initial at an underlying level. He claims that a language such as Japanese is truly head-final, since the mass movement which would be required to take an underlying head-initial structure to the head-final ones actually found in such languages would violate other constraints. It is implied that such languages are likely following a head-final parameter value, as originally conceived. (For a head-initial/Antisymmetry analysis of Japanese, see Kayne 2003.)
Takita's argument is based on the analysis provided by Lin concerning Chinese (see above). Since surface head-final structures are derived from underlying head-initial structures from the act of moving the complements, further extraction from within the moved complement violates CED.
One of the examples of movement which Takita looks at is that of VP-fronting in Japanese. Grammatically, there is not a significant difference between the sentence without VP-fronting (a) and the sentence where the VP moves to the matrix clause (b).
a. [CP1 Taro-ga [CP2[IP2 Hanako-ga [VP2 hon-o sute]-sae sita to] omotteiru] Taro-NOM Hanako-NOM book-ACC discard-even did C think 'Taro thinks [that Hanako [even discarded his books]]' (Takita 2009 57: (33a) b. [CP1[VP2 Hon-o sute]-saei Taro-ga [CP2[IP2 Hanako-ga sita] to] omotteiru book-ACC discard-even Taro-NOM Hanako-NOM did C think '[Even discarded his books], Taro thinks [that Hanako did ti]' (Takita 2009 57: (33b)
In (b), the fronted VP precedes the matrix subject, confirming that the VP is located in the matrix clause. If Japanese were underlyingly head-initial, (b) should not be grammatical because it allows for extraction of an element (VP2) from the moved complement (CP2).
Thus Takita shows that surface head-final structures in Japanese do not block movement, as they do in Chinese. He concludes that, because Japanese does not block movement as shown in previous sections, it is a genuinely head-final language, and not derived from an underlying, head-initial structure. These results imply that Universal Grammar is equipped with the binary head-directionality, and is not antisymmetric. Takita briefly applies the same tests to Turkish, another seemingly head-final language, and finds similar results.
Some scholars, such as Tesnière, argue that there are no absolute head-initial or head-final languages. According to this approach, it is true that some languages have more head-initial or head-final elements than other languages do, but almost any language contains both head-initial and head-final elements. Therefore, rather than being classifiable into fixed categories, languages can be arranged on a continuum with head-initial and head-final as the extremes, based on the frequency distribution of their dependency directions. This view was supported in a study by Haitao Liu (2010), who investigated 20 languages using a dependency treebank-based method. For instance, Japanese is close to the head-final end of the continuum, while English and German, which have mixed head-initial and head-final dependencies, are plotted in relatively intermediate positions on the continuum.
Polinsky (2012) identified the following five head-directionality sub-types:
- Rigid head-final languages, including Japanese, Korean and Tamil;
- Non-rigid head-final languages, including Latin, German, Persian, Basque, Tsez and Avar;
- Clearly head-initial languages, including Irish, Malagasy, Tongan and most Mayan languages;
- "SVO/head-initial" languages, including Indonesian and Yucatec Mayan;
- "SVO sundry", including English, Russian, the Romance languages and Bantu languages.
She identified a strong correlation between the head-directionality type of a language and the ratio of verbs to nouns in the lexical inventory. Languages with a scarcity of simple verbs tend to be rigidly head-final, as in the case of Japanese, whereas verb-rich languages tend to be head-initial languages.
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