One of the ideas which Comte most admires in Condorcet, and which he regards as indispensable to social science, is that which makes a single being in process of evolution of the totality of the human species.[237] Henceforth, the parallelism between this immense “social unity,” and the organisms studied by biology could not be a strict one. “The complex nature of the former,” says Comte himself, “deeply differs from the indivisible constitution of living beings.” We must then know how to restrain comparison wisely, “in order that it should not give rise to faulty approximations, instead of precious indications.” Comte has sometimes failed in carrying out this prudent precept, for instance, when in the social organism he looks for what is analogous to tissues, organs, and systems studied by the anatomists. But he has, none the less, traced very firmly the limits beyond which the use of analogy here becomes an abuse. These limits are determined by the specific character of the social reality, which escapes the grasp of the biological method. For the principal phenomenon in sociology, the one which establishes most evidently its scientific originality, is the gradual and continuous influence of human generations upon one another. Now our intelligence cannot “guess the principal decisive phases of such a complex evolution without an historical analysis properly so-called.”[238] Here is the final word: no history, no sociology. Comte had already written in 1822: To reduce sociology to biology is to annul the direct observation of the social past. Undoubtedly the reason for man’s superiority over the other animals lies in the relative perfection of his organisation. In this sense, social physics, that is to say, the study of collective development of the human species, is really a branch of physiology. In this sense, the history of civilisation is but the sequel and the indispensable complement of the natural history of man. But, important as it is to form a proper conception, and never to lose sight of this relation, yet it would be a mistake to conclude from it that no clear division should be established between social physics and physiology properly so-called. For, in the case of the human race, there is history _which cannot be reached by a process of deduction_.[239] III. Already, in biology the nature of the object had compelled scientific men to start from the consideration of the whole to reach that of the parts, to proceed from the complex to the simple. With still greater reason, the same inversion of method imposes itself in sociology. For, although the individual elements of society appear to be more separable than those of the living being, the social _consensus_ is still closer than the vital _consensus_.[240]