Methods and systems consistent with the present invention provide an improved IR system that performs information retrieval by using probabilities. When performing information retrieval, the improved IR system utilizes both the prior probability that a document is relevant independent of the query as well as the probability that the query was generated by a particular document given that the particular document is relevant. By using these probabilities, the improved IR system retrieves documents in a more accurate manner than conventional systems which are based on an ad hoc approach.