Montague grammar
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Montague grammar is an approach to natural language semantics, named after American logician Richard Montague. The Montague grammar is based on formal logic, especially higher-order predicate logic and lambda calculus, and makes use of the notions of intensional logic, via Kripke models. Montague pioneered this approach in the 1960s and early 1970s.
Overview
Montague's thesis was that natural languages and formal languages can be treated in the same way:
There is in my opinion no important theoretical difference between natural languages and the artificial languages of logicians; indeed, I consider it possible to comprehend the syntax and semantics of both kinds of language within a single natural and mathematically precise theory. On this point I differ from a number of philosophers, but agree, I believe, with Chomsky and his associates.
Montague published what soon became known as Montague grammar in three papers:
- 1970: "Universal grammar"
- 1970: "English as a Formal Language"
- 1973: "The Proper Treatment of Quantification in Ordinary English"
Illustration
Montague grammar can represent the meanings of quite complex sentencescompactly. Below is a grammar presented in Eijck and Unger's textbook.
The types of the syntactic categories in the grammar are as follows, with t
denoting a term and f denoting a formula.
| category | symbol | type |
| Sentence | S | |
| Verb phrase | VP | |
| Noun phrase | NP | |
| Common noun | CN | |
| Determiner | DET | |
| Transitive verb | TV |
The meaning of a sentence obtained by the rule is obtained by
applying the function for NP to the function for VP.
The Types of VP and NP might appear a bit unintuitive: why is the meaning of a noun phrase not simply a term? This is because meanings of many noun phrases, such as "the man who whistles", is not just a term in predicate logic, but also includes a predicate for the activity, like "whistles", which cannot be represented in the term So we need some term, for example x, and a formula whistles to refer to the man who whistles. The meaning of verb phrases VP can be expressed with that term, for example stating that a particular x satisfies sleeps snores. Now the function associated with NP takes that kind of function and combines it with the formulas needed to express the meaning of the noun phrase. Note that this particular way of typing NP and VP is not the only possible one.
The important thing here is that the meaning of an expression is obtained as a function of its components, either by function application or by constructing a new function from the functions associated with the component. This compositionality makes it possible to assign meanings reliably to arbitrarily complex sentence structures, with auxiliary clauses and many other complications.
The meanings of other categories of expressions are either similarly function applications, or higher-order functions. The following are the rules of the grammar, with
the first column indicating a non-terminal symbol, the second column one possible
way of producing that non-terminal from other non-terminals and terminals,
and the third column indicating the corresponding meaning.
| meaning | ||
| S | NP VP | |
| NP | name | |
| NP | DET CN | |
| NP | DET RCN | |
| DET | "some" | |
| DET | "a" | |
| DET | "every" | |
| DET | "no" | |
| VP | intransverb | |
| VP | TV NP | |
| TV | transverb | |
| RCN | CN "that" VP | |
| RCN | CN "that" NP TV | |
| CN | predicate |
Here are example expressions and their associated meaning according to the above grammar.
You can look at how the meaning of a given sentence is formed from its constituent
expressions, either by forming a new higher-order function, or by applying
a higher-order function for one expression to the meaning of another.
| expression | meaning |
| a | |
| man | |
| a man | |
| sleeps | |
| a man sleeps | |
| man that dreams | |
| a man that dreams | |
| a man that dreams sleeps |
The following are other examples of sentences translated into the predicate logic by the grammar.
| sentence | translation to logic |
| Jill sees Jack | |
| every woman sees a man | |
| every woman sees a man that sleeps | |
| a woman that eats sees a man that sleeps |