1. A method, comprising: receiving, by one or more computers, a current search query during a current search session; determining, by one or more computers and based on a difference between terms of the current search query and terms of a previous search query received during the current search session, that the current search query is an attempt to refine the previous search query; identifying, by one or more computers and based on the determination that the current search query is an attempt to refine the previous search query, a set of related terms based on a given term that is included in the previous search query, but not included in the current search query; determining, by one or more computers and based on search log data for previous search sessions, that the given term was replaced with a different term from the set of related terms in at least a specified portion of the previous search sessions; in response to the determination that the given term was replaced with the different term from the set of related terms, generating a modified search query that includes the different term; and providing the modified search query for presentation in a display of a user device corresponding to the current search session.