 The second pillar of positive philosophy, the law of the classification of the sciences, has withstood the test of time much better than the law of the three stages. Of the various classifications that have been proposed, it is Comte’s that is still the most popular today. This classification, too, structures the Course, which examines each of the six fundamental sciences—mathematics, astronomy, physics, chemistry, biology, sociology—in turn. It provides a way to do justice to the diversity of the sciences without thereby losing sight of their unity. This classification also makes Comte the founder of the philosophy of science in the modern sense. From Plato to Kant, reflection on science had always occupied a central place in philosophy, but the sciences had to be sufficiently developed for their diversity to manifest itself. It was thanks to his education at the École Polytechnique that Comte, from 1818, began to develop the concept of a philosophy of science. At about the same time Bolzano wrote his Wissenschaftslehre (1834) and Mill his System of Logic (1843), Comte’s Course presented in sequence a philosophy of mathematics, of astronomy, of physics, of chemistry, of biology, and of sociology. Comte’s classification is meant not to restore a chimerical unity, but to avoid the fragmentation of knowledge. Thanks to it, the sciences are related to one another in an encyclopedic scale that goes from the general to the particular, and from the simple to the complex: moving from mathematics to sociology, generality decreases and complexity increases.