8. A non-transitory computer-readable storage medium comprising instructions, which, when executed by one or more computers, cause the one or more computers to perform operations of: receiving a first term, a second term, and a third term; determining that a phrase that includes the first term, the second term, and the third term has a collective meaning that is different than each of a meaning of the first term, a meaning of the second term, and a meaning of the third term; in response to determining that the phrase that includes the first term, the second term, and the third term has a collective meaning that is different than each of the meaning of the first term, the meaning of the second term, and the meaning of the third term: identifying, in a collection of search queries, an original search query that includes: (i) the phrase that includes the first term, the second term, and the third term, and (ii) an additional, original search query term that is not included in the phrase; determining a number of times that, in the collection of search queries, the original query that includes (i) the phrase that includes the first term, the second term, and the third term, and (ii) the additional, original search query term that is not included in the phrase, is followed by a revised search query that includes: (i) the phrase that includes the first term, the second term, and the third term, and (ii) an additional, revised search query term that is different than the additional term and that is not included in the phrase; and determining, based on the number of times, whether to revise a subsequently received search query that includes: (i) the phrase that includes the first term, the second term, and the third term, and (ii) the additional, original search query term, to include the additional, revised search query term.
8. A non-transitory computer-readable storage medium comprising instructions, which, when executed by one or more computers, cause the one or more computers to perform operations of: receiving a first term, a second term, and a third term; determining that a phrase that includes the first term, the second term, and the third term has a collective meaning that is different than each of a meaning of the first term, a meaning of the second term, and a meaning of the third term; in response to determining that the phrase that includes the first term, the second term, and the third term has a collective meaning that is different than each of the meaning of the first term, the meaning of the second term, and the meaning of the third term: identifying, in a collection of search queries, an original search query that includes: (i) the phrase that includes the first term, the second term, and the third term, and (ii) an additional, original search query term that is not included in the phrase; determining a number of times that, in the collection of search queries, the original query that includes (i) the phrase that includes the first term, the second term, and the third term, and (ii) the additional, original search query term that is not included in the phrase, is followed by a revised search query that includes: (i) the phrase that includes the first term, the second term, and the third term, and (ii) an additional, revised search query term that is different than the additional term and that is not included in the phrase; and determining, based on the number of times, whether to revise a subsequently received search query that includes: (i) the phrase that includes the first term, the second term, and the third term, and (ii) the additional, original search query term, to include the additional, revised search query term. 9. The non-transitory computer-readable storage medium of claim 8 , wherein the one or more computers are further configured to perform operations comprising: determining whether to generate a substitution rule based on the number of times and the collective meaning of the phrase that includes the first term, the second term, and the third term; and generating and storing the substitution rule in response to determining that the substitution rule is to be generated.