This research paper discusses one of the principal aspects of a project recently funded by the Applications of Computers to Manufacturing Engineering (ACME) Directorate of the SERC. The work is concerned with the initial phase in mechanical engineering design of problem elaboration from recognition of a need via an issued design brief to the generation of full requirement specifications. The intention is to present a basic theoretical process through which it should be possible to expand different sorts of briefs by means of a reasonably generalized process, thus making the process somewhat independent of the specific nature of the design problems for which it is used. Considerable attention has been paid to the work of others in this area and a review of this is presented in the introduction so that a context for the work is provided at the outset. The system discussed in the paper is meant to be implemented on a computer and considerable work has already been carried out on this front. It is the view of the authors that the theory of the process has had to evolve simultaneously with the computer implementation, so that concepts and ideas could be tried out and validated wherever possible. The issue of validation is clearly most important and further work is on-going and planned to develop it to the point where significant problem generalization is feasible.