A novel method for going beyond the observed properties of a keyword, to a model in which the presence of a term in a document is assessed not by looking at the actual occurrence of that term, but by a set of non-independent supporting terms, defining the context. In other words, similarity is determined not by properties of the keyword, but by properties of the keyword's context. This yields a scoring for documents which is useful for ad hoc retrieval and, by extension, any information retrieval task where keyword-based similarity is needed.