The editor has offered the challenge of producing a review-type article which might introduce constructively provocative ideas into an area of hard tissue inquiry. He probably expected a review of BMU theory, but since that theory flourishes in the capable hands of others a different topic appears here, an algorithm little touched by but fully open to the armamentarium of modern skeletal research. The factors of need and timeliness which dictated its choice will receive brief comment in the Discussion section of this text. The following paragraphs place the topic in perspective and the text then addresses the main issue. Modern physicians probably memorize no more facts than Hippocrates did over 2000 years ago, yet our mastery of disease betters his, partly because man records knowledge by varied means to pass it on to his descendents. In this process each generation retains still useful knowledge, discards the outmoded, and adds its own contribution. This continually improves the quality of existing knowledge. But another factor promises greater mastery of disease than merely recording more facts, to wit: discovering and applying the principles of action underlying health and disease. Action principles can lead to the crux of complex problems with efficient, even seemingly magical use of memory, intellect, effort, and time, and they have transformed our whole science and technology, largely within the writer 's lifetime. Past transformations tended to follow a pattern. First data accumulate and undergo varied refinements but prove refractory to early efforts to understand them. Then, often when it seems the next generation can only add more decimals to existing knowledge, a newly formulated principle of action