Till about fifty years ago, he said, generalisations on man and society have erred by implicitly assuming that human nature and society will for ever revolve in the same orbit and exhibit virtually the same phenomena. This is still the view of the ostentatiously practical votaries of common sense in Great Britain; whereas the more reflective minds of the present age, analysing historical records more minutely, have adopted the opinion that the human race is in a state of necessary progression. The reciprocal action between circumstances and human nature, from which social phenomena result, must produce either a cycle or a trajectory. While Vico maintained the conception of periodic cycles, his successors have universally adopted the idea of a trajectory or progress, and are endeavouring to discover its law. [Footnote: Philosophical writers in England in the middle of the century paid more attention to Cousin than to Comte or Saint-Simon. J. D. Morell, in his forgotten History and Critical View of Speculative Philosophy (1846), says that eclecticism is the philosophy of human progress (vol. ii. 635, 2nd ed.). He conceived the movement of humanity as that of a spiral, ever tending to a higher perfection (638).] But they have fallen into a misconception in imagining that if they can find a law of uniformity in the succession of events they can infer the future from the past terms of the series. For such a law would only be an "empirical law"; it would not be a causal law or an ultimate law. However rigidly uniform, there is no guarantee that it would apply to phenomena outside those from which it was derived. It must itself depend on laws of mind and character (psychology and ethology). When those laws are known and the nature of the dependence is explained, when the determining causes of all the changes constituting the progress are understood, then the empirical law will be elevated to a scientific law, then only will it be possible to predict. Thus Mill asserted that if the advanced thinkers who are engaged on the subject succeed in discovering an empirical law from the data of history, it may be converted into a scientific law by deducing it a priori from the principles of human nature. In the meantime, he argued that what is already known of those principles justifies the important conclusion that the order of general human progression will mainly depend on the order of progression in the intellectual convictions of mankind. Throughout his exposition Mill uses "progress" in a neutral sense, without implying that the progression necessarily means improvement. Social science has still to demonstrate that the changes determined by human nature do mean improvement. But in warning the reader of this he declares himself to be personally an optimist, believing that the general tendency, saving temporary exceptions, is in the direction of a better and happier state. 8.