Abstract: Methods and systems for providing 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.