Social Dynamics regards sequences. But the _consensus_ in social facts prevents our tracing the leading facts in one generation to separate causes in a prior one. Therefore, we must find the law of the correspondence not only between the simultaneous states, but between the simultaneous changes of the elements of society. To find this law, which, when duly verified, will be the scientific derivative law of the development of humanity, we must combine the statical view of the phenomena with the dynamical. Fortunately, the state of mankind's speculative faculties and beliefs, being the prime agent of the social movement, furnishes a clue in the maze of social elements, since the order of human progression in all respects will mainly depend on the order of progression of this prime agent. That the other dispositions which aid in social progress (e.g. the desire for increased material comfort) owe their means of working to this (however relatively weak a propensity it may be) is a conclusion from the laws of human nature; and this conclusion is in accordance also with the course of history, in which internal social changes have ever been preceded by proportionate intellectual changes. To determine the law of the successive transformations of opinions all past time must be searched, since such changes appear definitely only at long intervals. M. Comte alone has followed out this conception of the Historical Method; and his generalisation, to the effect that speculation has, on all subjects, three successive stages, has high scientific value. The Historical Method will trace the derivative laws of social order and progress. It will enable us both to predict the future, and (thus founding the noblest part of the Political Art) partly to shape it. At present, both the Science and the Art are in the rudiments; but they are progressing. CHAPTER XI. THE LOGIC OF PRACTICE, OR ART; INCLUDING MORALITY AND POLICY. Practical Ethics, i.e. Morality, is an art; and therefore its Method must be that of Art in general. Now, Art from the major premiss, supplied by itself, viz. that the end is desirable, and from the theorem, lent by Science, of the combinations of circumstances by which the end can be reached, concludes that to secure this combination of circumstances is desirable; if it also appear practicable, it turns the theorem into a rule. Unless Science's report as to the circumstances is a full one, the rule may fail; and as, in any case, rules of conduct cannot comprise more than the ordinary conditions of the effect (or they would be too cumbrous for use), they must, at least in moral subjects, be considered, till confronted with the theorems, which are the reasons of them, provisional only. Practical maxims, therefore, till so confronted, are not universally true even for a given end, much less for conduct generally, and must not be used, as they are by the _geometrical_ school, as ultimate premisses.