REMOVING SUBSTITUTION RULES

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for removing substitution rules. According to one implementation, a method includes identifying a revised search query that was revised to include a substitute term of a query term; identifying search results that were generated using the revised search query, wherein each search result references a resource; determining, by one or more computers, that none of the resources referenced by a subset of the search results include the substitute term of the query term; and in response to determining that none of the resources referenced by the subset of search results include the substitute term of the query term, incrementing a no-match score for the substitute term.