Locality (linguistics)

In linguistics, locality is the proximity of elements in a linguistic structure. Constraints on locality limit the span over which rules can apply to a particular structure. Theories of transformational grammar use syntactic locality constraints to explain restrictions on argument selection, syntactic binding, and syntactic movement.

Where locality is observed Locality is observed in a number of linguistic contexts, and most notably with:

Selection of arguments; this is regulated by the projection principle Binding of two DPs; this is regulated by binding theory Displacement of wh-phrases; this is regulated by wh-movement

Selection The projection principle requires that lexical properties — in particular argument structure properties such as thematic roles — be "projected" onto syntactic structures. Together with Locality of Selection, which forces lexical properties to be projected within a local projection (as defined by X-bar theory), the projection principle constrains syntactic trees. Syntactic trees are represented through constituents of a sentence, which are represented in a hierarchical fashion in order to satisfy locality of selection through the restraints of X-bar theory. In X-bar theory, immediate dominance relations are invariant, meaning that all languages have the same constituent structure. However, the linear precedence relations can vary across languages. For example, word order (i.e. constituent order) can vary with and across languages.

If α selects β, then β depends on α. If α selects β, and if locality of selection is satisfied, then α and β are in a local dependency. If α selects β, and if locality of selection is not satisfied, then α and β are in a non-local dependency. The existence of a non-local dependency indicates that movement has occurred. From the perspective of projection, an element can be "stretched" to occupy the following projection levels:

Minimal (X) Intermediate (X') Maximal (X max) These occupying elements appear valid for all syntactically relevant lexical and functional categories.

Head-complement selection

According to locality of selection, the material introduced in the syntactic tree must have a local relationship with the head that introduces it. This means that each argument must be introduced into the same projection as its head. Therefore, each complement and specifier will appear within the local projection of the head that selects it. For example, the contrast between the well-formed (1a) and the ill-formed (1b) shows that in English, an adverb cannot intervene between a head (the verb study) and its complement (the DP the report).

In structural accounts of the contrast between (1a) and (1b), the two sentences differ relative to their underlying structure. The starting point is the lexical entry for the verb study, which specifies that the verb introduces two arguments, namely a DP which bears the semantic role of Agent, and another DP which bears the semantic role of Theme.

lexical entry for study: V, <DPAGENT,DPTHEME>

In the tree for sentence (1a), the verb, studies, is the Head of the VP projection, the DPTHEME, the report, is projected onto the Complement position (as sister to the head V), and the DPAGENT , John, is projected onto the Specifier (as sister to V'). In this way, (1a) satisfies Locality of Selection as both arguments are projected within the projection of the head that introduces them. The adverb phrase, AdvP carefully attaches as an unselected adjunct to VP; structurally this means that it is outside of the local projection of V as it is sister to and dominated by VP. In contrast, in the tree for sentence (1b), the introduction of the AdvP carefully as sister to the verb study violates Locality of Selection; this is because the lexical entry of the verb study does not select an AdvP, so the latter cannot be introduced in the local projection of the verb.

Morphological selection Locality can also be broken down into a morphological perspective, by analyzing words with some, or many affixes. A speaker who can make sense of a word with many morphemes (e.g. affixes) must know: how the morpheme is pronounced and what kind of morpheme it is, (free, prefix, suffix). If it is an affix, then the speaker also must know what the affix c-selects. The speaker must also know that the c-selected element must be adjacent to the affix, amounting to the requirement that branches of a tree never cross. Crossing branches is not included in the lexicon, and it is a general property of how linguistic structures are grammatically structured. This is true because lexical entries do no impose a requirement on a part of word structure that it is not sister to. This relates to the fact that affixes cannot c-select for an element which is not a sister. Additionally, the speaker must know what kinds of thing results after c-selection. These key aspects that a speaker must know can be observed in the lexical entries below, with the example "denationalization".

Lexical selection When meeting selection requirements, the semantic content of the constituent selected by the head must be taken into consideration. For example, the thematic role of the constituent that is selected, and the properties of the head which selects it. Take, for example, the verb head elapse, which selects for a DP subject. E.g. a) *[DP Johnagent] elapsed. b) [DP Timeagent, can elapse] elapsed. However, while [DP John] is syntactically in subject position, it gives an ungrammatical sentence as [DP John] cannot elapse, it has no thematic quality to elapse, and as such cannot meet the lexical selection requirements of [VP elapse]. However, [DP Time] in subject position does have this thematic quality and can be selected by [VP elapse]. Lexical selection is specific to individual word requirements, these must abide to both Projected Principle and Locality requirements.

Detecting selection Crucially, selection determines the shape of syntactic structures. Selection takes into consideration not only lexical properties but also constituent selection, that is what X-Bar Theory predicts as appropriate formulations for specific constituents.

Covariation One way to determine which syntactic items relate to each other within the tree structure is to examine covariances of constituents. For example, given the selectional properties of the verb elapse, we see that not only does this verb select for a DP subject, but is specific about the thematic role this DP subject must have.

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