In m a n y applications of natural language processing it is necessary to determine the likelihood of a given word combination. For example, a speech recognizer m a y need to determine which of the two word combinations "eat a peach" and "eat a beach" is more likely. Statistical NLP methods determine the likelihood of a word combination according to its frequency in a training corpus. However, the nature of language is such that m a n y word combinations are infrequent and do not occur in a given corpus. .
