# ID/LP grammar

An ID/LP grammar is a formal grammar that distinguishes immediate dominance (ID) constraints from linear precedence (LP) constraints. Whereas traditional phrase structure rules incorporate dominance and precedence into a single rule, ID/LP maintains separate rule sets which need not be processed simultaneously. ID/LP grammars are used in computational linguistics.

For example, a typical phrase structure rule might say ${\displaystyle {\ce {S->NP\;VP}}}$, indicating that an S-node dominates an NP-node and a VP-node, and that the NP precedes the VP in the surface string. In ID/LP grammars, this rule would only indicate dominance, and a separate rule indicating linear precedence, such as ${\displaystyle {\ce {[NP,VP]}}}$, would also be given.

The idea first came to prominence as part of generalized phrase structure grammar;[1][2] the ID/LP approach is also used in head-driven phrase structure grammar,[3] lexical functional grammar, and other unification grammars.

Current work in the Minimalist Program also attempts to distinguish between dominance and ordering. For instance, recent papers by Noam Chomsky have proposed that, while hierarchical structure is the result of the syntactic structure-building operation Merge, linear order is not determined by this operation, and is simply the result of externalization (oral pronunciation, or, in the case of sign language, manual signing).[4][5][6]