This classification is confirmed, in fact, by the general usage of learned men. It reproduces the historic order of the development of the sciences. Thus, for a long time, mathematics was the only science of a positive type. On the other hand, social science has been the last to reach this point. Nevertheless, Comte does not mean to say that the fundamental sciences came into existence one after the other, nor that, for every one of them, each period is sufficiently explained by the period immediately preceding it. His thought is very different. On the contrary, he represents the development of the several sciences as simultaneous. They act and react one upon another in a thousand ways. Often some progress in a science is the direct effect of a discovery made in an art which has apparently no affinities with it. Such is, to quote an example which Comte could not in the least have foreseen, the progress of astronomical observations due to photography. In fact, the history of a science during a given period is closely allied to that of the other sciences and arts during the same time, or rather, to be more explicit, to the general history of civilisation. But their respective transitions to the positive state is accomplished in the order set forth in the classification. For individually they could not reach this state, if the fundamental science immediately preceding had not attained to it before them. “It is in this order that the progress, although simultaneous, must have taken place.”[25] III. Mr. Herbert Spencer has made several objections to Auguste Comte’s classification of the sciences; Littré has lengthily refuted them. It is not in our design to reopen this discussion. But it results from the preceding explanations that the greater number of Mr. Spencer’s criticisms miss the mark, perhaps because he has not read Comte properly. On his own admission, he only knows the two first lessons in the _Cours de philosophie positive_ in the text, further the inorganic Physics and the first chapter of the Biology in Miss Martineau’s condensation, and finally the remainder in Lewes’s summing up in his _History of Philosophy_.[26] If Mr. Spencer had been able to obtain a knowledge of the _Cours de philosophie positive_ in its entirety, and especially of the three last lessons, or at least of the _Discours sur l’Esprit positif_ or of the _Discours sur l’ensemble du positivisme_ he would probably have appreciated differently the positive classification of the sciences. His own classification, in which he includes the concrete and concrete-abstract sciences, is not really opposed to that of Auguste Comte who only wished to classify the fundamental _abstract_ sciences. Comte never sought to do what Mr. Spencer reproaches him with not having done. Among Mr. Spencer’s objections, there is one which, bearing upon the very conception of the classification of the sciences, shows very clearly the misunderstanding which we are pointing out.