Locality (linguistics)

In linguistics, locality refers to 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.

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

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.

According to locality of selection, whatever is 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.

In the tree for sentence (1a), the verb is the Head of the VP projection, the DP_THEME is projected onto the Complement position (as sister to the head V), and the DP_AGENT 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. In addition, the 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.

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