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.”