Head directionality parameter

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.

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:

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.

English is a strongly head-initial language. In a typical verb phrase, for example, the verb precedes its complements, as in the following example:

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