The theory of perception which Comte opposes to the abstract sensualism of the ideologists is allied to his general conception of the relations between the subject and the object. Our internal operations are never anything but the direct or indirect prolongation of our external impressions. But “reciprocally, the latter are always complicated by the others, even in the most elementary cases.” The sensation, which appears simple, is already the result of a very complex combination.[200] For no sensations are really perceived except after reiterated impressions. If the mind is ever passive, it can only be the first time. For the second, it is already prepared by the preceding one, combined with the whole of previous acquisitions. And Comte insists upon “the habitual participation of reasoning in the operations which are attributed to sensation alone.” The activity belonging to the mind enters into all its actions, even the smallest of them. Mental pathology scarcely exists, owing to the lack of the scientific spirit among specialists for the diseases of the mind. Still if Broussais’ principle be true, that is to say, if morbid phenomena are produced according to the same laws which govern normal phenomena, what advantage might not scientific men derive from the observation of mental diseases? They are privileged cases which nature supplies for them, real experiments, where that which is inseparable in the normal state appears disassociated. What light might be thrown by this means upon many physiological and even anatomical questions, in particular in what concerns the sentiment of the _ego_ (diseases of personality, aboulia, etc.), and the faculties of expression, isolated from the faculties of conception (diseases of speech). Animal psychology would not be less instructive. All the affective and intellectual faculties are common to men and higher animals, save perhaps the highest intellectual aptitudes. Even this exception is a doubtful one, if without prejudice we compare the actions of the highest animals with those of the least developed savages. We should study the habits and the mind of wild animals. We should observe the changes which are produced in them by domestication. Here again almost everything has to be done afresh.[201] IV.