However, if this abstract historical method were used by the sociologist to the exclusion of every other, he would sometimes come to a wrong conclusion, and take the continuous decrease in a natural faculty for a tendency to total extinction. For instance, as civilisation becomes more refined, man eats less than formerly. Nobody concludes from this that he tends not to eat at all. But the absurdity which is palpable here, might, in other cases pass unperceived. That is why the historical method in sociology requires to be controlled by the positive theory of human nature. All the inductions which might contradict this theory are to be rejected. Indeed, the whole social evolution is at bottom but a simple development of humanity, without the creation of new faculties. The germ, at any rate, of all the dispositions or effective faculties which sociological observation, (and in particular, history), may make known, must then be found in the primordial type which biology has constructed beforehand for sociology. Accordance between the conclusions of historical analysis and the preliminary notions of the biological theory is the indispensable guarantee of sociological demonstrations.[247] V. Thus conceived the historical method rests upon the postulate given by Comte, as we have seen, as a basis to his sociology. This postulate is thus enunciated: _The nature of man evolves without being transformed._ The various physical, moral and intellectual faculties, must be found the same at all the degrees of historical evolution, and always similarly co-ordinated among themselves. The development which they receive in the social state can never change their nature, nor consequently destroy or create any one of them, nor even intervene in the order of their importance. In a word, the chief regulator of sociology is the science of human nature. It can even be said, without forcing the meaning of Comte’s thought, that sociology is really a psychology:[248] not indeed, it is true, a psychology founded upon the introspective analysis of the individual subject, but a psychology whose object is the analysis by history, of the universal subject, that is to say, of Humanity.