Comte endeavours to bring the complexity and the extreme variety of social phenomena into an intelligible unity. This complexity is such that we could not determine the laws by starting from the observation of the simplest phenomena to reach the more complex ones afterwards. Moreover, these facts only possess sociological significance if the observer is already provided with a general theory before he ascertains them. But, on the other hand, history cannot be deduced. Given an already positive knowledge of human nature and of the “_milieu_” in which it evolves, we could not say _a priori_ how it will evolve. History must then teach us how, as a matter of fact, social life has developed Humanity. Nevertheless, once this concession has been made to observation the method becomes again deductive. Since sociology is a science it ought, like the other sciences, to be able to substitute rational prevision to the empirical establishment of facts. To complete the characterising of this final science, it must be at once positive, like the subjacent fundamental sciences, and universal like philosophy, which alone up to the present time has looked at things from “the point of view of the whole.” Henceforth these two conditions are fulfilled. In the first place, the positivity of sociology cannot be doubted. In it social facts are conceived as subject to laws, and Comte abstains from any research as to their mode of production. Then, sociology, in spite of the extreme difficulties of its object, has assumed the deductive form, and has brought secondary laws under more general laws. Comte is even convinced that his sociology comes nearer to the perfect scientific form than physics or chemistry. By his discovery of the great dynamic law of the three states, has he not given it a unity which is to be found as complete nowhere else but in astronomy? But, at the same time, it is truly universal, since it is a philosophy of history, or, in other words, the science of humanity considered in its evolution. As this science presupposes biology, and as biology in turn presupposes the science of the “_milieu_” in which living beings are immersed, sociology becomes at once the summary and the crown of the sciences which precede it. Thus in replacing man in Humanity, and Humanity in the system of its conditions of existence, Comte constructs a final science which is at the same time the supreme science, the only science, that is to say, philosophy. “If the laws of sociology could be sufficiently known to us, they alone would suffice to replace all the others, save the difficulties of deduction.”[249] The science of Humanity is the centre around which the others range themselves in order.