A facility for attributing subject categories to documents in a set of documents collected on behalf of the user is described. For each document in the set of documents, based on semantic analysis of the document, the facility identifies one or more direct subjects for the document. The facility attributes to the document the direct subjects identified for the document. Based on semantic analysis across the documents of the set, the facility identifies one or more collective subjects each for a proper subset of the set of documents. The facility attributes each identified collective subject to each document of the subset of the set of documents for which it was identified.