Abstract: An approach is provided expand queries processed by a question/answer (QA) system. In the approach, concepts are extracted from documents using natural language processing to identify the concepts included in passages found in the documents. The approach generates child level categories in a category hierarchy from the concepts and groups the child level categories into sets based on related concepts. The process creates parent categories from the sets and divides a corpus used by the QA system into a number of sub-corpora, with each of the sub-corpora corresponding to one of the child level categories. The approach answers questions posed to the QA system by identifying a child level category related to the question and searching the sub-corpora corresponding to the child level category.