II.
Henceforth, the fundamental sciences are all conceived as equally positive. They have all given up the pursuit of the absolute for the study of the relative, and the search after causes for the knowledge of laws. All now proceed by means of the same general methods and their differences can therefore only arise from their object, that is to say from the nature of the phenomena which are studied. Consequently their relations of mutual dependence will solely result from the relations of these phenomena. Now, observation shows us that these phenomena form themselves into a certain number of natural categories, such that the rational study of each category presupposes a knowledge of the laws of the preceding category, and that a knowledge of this one is in turn presupposed for understanding the one that follows. This order is determined by the degree of generality of the phenomena, from which their successive dependence upon each other results, and as a consequence the greater or lesser simplicity of each science results from it also.
Upon this principle, the encyclopædic ladder of the fundamental sciences is easily constructed. After the mathematics, in an order of diminishing generality and of growing complexity, come astronomy, physics, chemistry, physiology or biology, social physics or sociology. The first science considers the most general, the most simple, the most abstract phenomena, and those furthest removed from humanity. They influence all the others, without being influenced by them. The phenomena considered by the last are the most particular, the most complicated, the most concrete, and the most directly interesting for man; they depend more or less upon all the preceding ones. “Between these two extremes, the degrees of specialisation, of complication, and of individualisation, are in an ever-growing quantity.”
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]