Phrase-Structure Rules: Theoretical Foundations (Sag et al., Ch. 2)

1. Phrase-Structure Rules: Theoretical Foundations(Sag et al., Ch. 2) Linguistics 6450 January 24, 2008

2. Basic Concepts and Terms • A phrase-structure (or PS) rule describes a constituent: a string of words that behaves as a unit, e.g., PP  P NP. • All PS rules are translatable into hierarchical representations called local trees:

3. Basic Concepts and Terms • The top node in each local tree is its mother node; the top mother nodeis the root node. • The mother node of a local tree can be an XP (maximal) node, an X’ (intermediate) node or an X (lexical or X0) node. • The nodes immediately below the mother are daughter nodes. • Every daughter has a unique mother, but a mother can have several daughters, in which case the mother is a branching node.

4. Basic Concepts and Terms • Nodes typically have two branches (are binary branching). • VP can have up to three branches, depending on the number of complements the verb has. • Examples? • What about adjuncts? • If two nodes are dominated by the same mother, we call them sisters. • If you can trace a path down from a node A to a node B, we say that A dominates B.

5. Basic Concepts and Terms • The words are sometimes called leaves. • The line that contains the words is called the terminal string. • A tree structure shows successive embeddings (‘daughter of the daughter of the daughter of…’) • A tree is a record of a derivational history: successive application of an applicable PS rules at each node. • However, a PS rule represents a mother-daughter relationship—not, say, a mother-grandaughter relationship.

6. What’s a Head? • Implicit here is the assumption that all licensing by heads is of sisters, not (say, nieces). • The rule *PP  P NP  (D) N’ is not a well formed PS rule.

7. Example

8. What are PS Rules for? • PS rules (or ‘rewrite rules’) are the engines that drive generative grammar. • Generative grammar was first proposed by Chomsky (1957), who described it as a device that produces all of the acceptable sentences of the language under analysis and none of the unacceptable ones. • A generative grammar is construed as a model of what it is the speaker appears to know.

9. Generative Grammar • Generative grammar is a model of discrete infinity: • It contains a finite number of rules (PS rules). • It contains a finite number of symbols (words); this is its lexicon. • These jointly produce an infinite number of sentences. • Because it is intended to account for sentences beyond the corpus, a generative grammar is not merely descriptive, but also predictive.

10. Prediction Makes the Grammar a Scientific Theory Any scientific theory is based on a finite number of observations, and it seeks to relate the observed phenomena and to predict new phenomena by constructing general laws in terms of hypothetical constructs [...]. Similarly, a grammar of English is based on a finite corpus of utterances (observations), and it will contain certain grammatical rules (laws) stated in terms of the particular phonemes, phrases, etc., of English (hypothetical constructs). The rules express structural relations among the sentences of the corpus and the indefinite number of sentences generated by the grammar beyond the corpus (predictions). (Chomsky 1957: 49)

11. What’s Beyond the Corpus • The sentences generated by a generative grammar include those that we have never uttered before and probably never will utter. • So, a grammatical sentence is distinct from an acceptable sentence or an easily processed sentence: • Garden-path sentences: The horse raced past the barn fell. • Center embedding:

12. Unspeakable Sentences • Another type of grammatical but unacceptable sentence: sentences of infinite length. • Infinity has two sources: • Iteration: • Recursion: the mother or grandmother node is the same as a daughter node, e.g., V’ V’ PP.