1. A method of retrieving computerized documents from a document database in a computer memory comprising the steps of: retrieving documents according to a first search statement; developing signatures for a plurality of documents by searching for words in the documents and removing common words which occur in a relatively high frequency in a natural language in which the documents are written; automatically associating selected ones of the documents with a first document according to a degree of match of the signatures of the selected documents with the signature of the first document; displaying the first document; responsive to a user indication that a second search is to be made, automatically selecting a set of words from an aggregate signature based on the signatures of the first and associated documents and the aggregate number of occurrences of the set of words in the first and associated documents; and constructing a second search statement from the selected set of words.