A Logical Approach

Newton's Third Rule of Philosophizing has recently been investigated from several points of view: by studying the vicissitudes of its metamorphosis from “hypothesis” to “rule,” the fact of its augmentation by four sentences in the third edition of the Principia, the Aristotelian and neo-scholastic flavor of some of its language, the scholarly significance of its editorial history. All these investigations have been carried on with relatively little concern for the actual intellectual content of the rule itself. The following analysis is intended to supplement and not to replace the studies previously undertaken. The supplement, however, is a necessity, not a luxury, and the historian can neglect it only at his own loss.

What does the rule actually say? Here too the discussion will start with a quotation of the standard English translation, but that will not be followed by a comparison with previous English translations, other language translations, the Latin text of the third edition, that of the second, that of the first, the various drafts of it that can be found among Newton's private papers, and other analogous rules and principles formulated by Newton's contemporaries, predecessors, and successors. Instead I shall proceed to analyze the rule logically, which too could be regarded as a comparison of sorts, a comparison with certain ideals and universals present in the human mind. In my view this kind of comparison — logical analysis — is prior to all the others.