The natural sciences are systems of empirical concepts, that is, of practical elaborations of knowledge, and, therefore, they do not belong to the sphere of theoretical, but to that of practical activity. This proposition must not be understood as referring to the practical ends, or applications, of science: action requires a knowledge of the individual fact with which we are to deal, and, therefore, the true antecedent of action is not science, but an individual (or historical) judgment. The natural sciences are not subservient to action, but they are actions in the service of knowledge. Because of the empirical and pragmatic character of their concepts, it is impossible either to unify them in a single concept, or to divide them according to rigorous distinctions. The natural laws which they evolve are the same empirical concepts, which give rise to the creation of classes and types, expressed in a different form; their empirical character is confirmed by what Boutroux called their contingency, which is nothing but the reflex of their arbitrary formation. Even the most general of those laws, that of the constancy and uniformity of nature, assumed as the foundation of so much pseudo-scientific thought in the nineteenth century, is a mere postulate of practical opportunity, without which it would be hardly possible to construct any science: it is the first economic principle of scientific method, not an attribute of objective reality. The truth of the natural sciences, that truth of which they and their empirical concepts are an abbreviated transcription, is the historical datum, the knowledge of actual individual happenings. History is the hot and fluid mass which the naturalist solidifies in the schematic moulds of classes and types. The naturalistic discoverer is, therefore, an historical discoverer and the revolutions of the natural sciences are steps in the progress of historical knowledge. The difference in method between history and the natural sciences is not due to the supposed difference between a higher and a lower reality (spirit and nature), or to the fact that nature has no history; nature is perpetual activity and change, that is, history, as much as the spirit, but the progress of nature is less clearly perceptible and less interesting to us than that of the human reality, and, therefore, an abbreviated transcription is more apt to satisfy our needs in relation to the knowledge of what we call nature than to that of the spirit. The nature that has no history, and which is opposed in dualistic systems of philosophy to the spirit of man, is not the actual, historical reality of nature, but the empirical concepts of the natural sciences, their classes, types and laws, conceived as an objective reality and substituted for that reality. In this sense, nature is not a special object, but only a method of treatment, as is proved by the fact that that same method, applied to the so-called higher and spiritual