Syntactic Theory

General Principles for Words and Phrases

Different versions of HPSG assume different principles concerning words and phrases.

In fact, Pollard and Sag 1994 also encoded the lexicon and the grammar rules as such principles.

For didactic purposes, this is not done here.

The Head Feature Principle (HFP)

The HFP is a central principle in HPSG. It guarantees that the syntactic category and the morphosyntactic properties of a phrase and its head daughter are identical.

The most general formulation of the HFP is:

The Head Feature Principle:
If there is a head-daughter, then the HEAD value of the mother and the HEAD value of the head daughter are identical.

The Valence Principle

This principle is used to allow for shorter formulations of the grammar rules.

In Sag/Wasow/Bender 2003 it is formulated as a default, i.e. as a principle that applies only if nothing else prevents it from applying.

The formulation in Sag/Wasow/Bender 2003, p.158:

The Valence Principle:
Unless the rules says otherwise, the mother's value for the VAL features (SPR, COMPS, and MOD) are identical to those of the head daughter.

For more formal remarks on the Valence Principle click here.

The Specifier-Head Agreement Constraint (SHAC)

The Specifier-Head Agreement Constraint guarantees agreement between the specifier and the head. This is needed for:

  • person and number agreement between the subject and a finite verb in a sentence.
    Pat walks/*walk, I am/*are/*is from Germany.
  • number agreement between a determiner and a head noun in a noun phrase.
    this book/*books, those books/*book

The effect of the SHAC can be summarized as follows:

Informal characterization of the Specifier-Head Agreement Constraint:
If a lexical element requires a specifier then it agrees with its specifier.
(i.e. the HEAD AGR value of the lexical element is identical with the HEAD AGR value of its specifier)

For more formal remarks on the SHAC click here.