1. A method for producing a phrase thesaurus, comprising the steps of: providing access to a thesaurus building computer coupled with a machine-readable phrase thesaurus database; identifying, by thesaurus building computer, a plurality of valid phrases that occur within a text corpus; determining, by thesaurus building computer, the degree of similarity between the valid phrases, wherein one or more contexts are created for each valid phrase, wherein each context for a valid phrase comprises a word or phrase that appears adjacent to the valid phrase in the text corpus, and wherein the degree of overlap of the contexts of each valid phrase with the contexts of each other valid phrase is determined; and grouping, in the phrase thesaurus database, the valid phrases into classes of equivalent valid phrases based upon the determined degree of similarity between valid phrases.
31. A method as in claim 1 , wherein the step of determining the degree of similarity between valid phrases further comprises the steps of: determining two or more of the degree of semantic similarity between valid phrases, the degree of syntactic similarity between valid phrases and the degree of pragmatic similarity between valid phrases; and combining the determinations of degree of similarity to produce an overall degree of similarity between valid phrases.