This dissertation presents a pragmatic interpreter/translator called Real English to serve as a natural language man-machine communication interface in a multi-mode on-line information retrieval system. This multi-mode feature affords the user a library-like searching tool by giving him access to a dictionary, lexicon, thesaurus, synonym table, and classification tables expressing binary relations as well as the document file representing the field of discourse. Real English will (1) syntactically analyze the user's message by means of a string analysis grammar to produce a tree representing the interrelationships of the grammatical entities comprising the message, (2) use this tree together with a pragmatic grammar to establish the set of commands necessary to fulfill the request, and (3) form the proper syntax for each command. The system is designed such that new linguistic discoveries may be incorporated by the grammarian without a major overhaul in the procedures. In the operation of the system the user is permitted to phrase his requests in any convenient form (i.e. declarative, imperative, interrogative, or fragmented sentence referred to as conversationally dependent sentences). Thus instead of placing the user in the difficult position of learning a new language, the system is given the responsibility of responding in and to the user's natural language. (Author/RM)