In this final part of the book several rules of discovery are considered, that is, non-deductive rules for finding hypotheses to solve problems. Of course, finding hypotheses is not a sufficient condition for discovery. The latter requires hypotheses to be plausible, and the plausibility test procedure of  Chapter 4 involves operations beyond simple hypothesis formation. Nevertheless, finding hypotheses is a necessary condition for discovery and, in that sense, one may speak of rules of discovery. The latter are not a closed set, given once for all, but rather an open set which can always be extended as research develops. Each such extension is a development of the analytic method, which grows as new non-deductive rules are added. As Bacon says, "the art of discovery may grow with discoveries."