While students of philosophy, although manifesting some doubt and dissatisfaction, allowed themselves to be intimidated by naturalism (dazzled, like the public, with technical applications, or confounded by the applause of the public), a tendency has become more and more accentuated during the last decades, which seems to us to offer great assistance to Logic and philosophy in general, if it is understood how to adapt it to its true end. It has not had any single centre of diffusion, but has arisen, almost contemporaneously, in several places, becoming at once diffused everywhere, like something that has happened at the right time. Several of its founders and promoters are mathematicians, physicists, and naturalists. From the very fact of their having begun to reflect upon their activity, these men have certainly ceased to be mere specialists, notwithstanding their protests to the contrary. Yet they obtain considerable strength from their specialism, finding in it a guide and a curb to prevent their losing sight in their gnoseological enquiry of the actual procedure of naturalistic constructions, which are its origin. The formula of this tendency is the recognition of the _practical or economic_ character of the mathematical, physical, and natural sciences. [Sidenote: _Avenarius, Mach._] The empirocriticism of Avenarius considers science to be a simple description of the forms of experience, and conceptual procedure to be the instrument that alters pure and primitive experience (pure intuition or pure perception) for the purpose of simplifying it. Ernest Mach has developed and popularized these views, for as a student of mechanics he had reached the same conclusions by his own path and in his own way. The physical sciences (he says), not less than zoology and botany, have as their sole foundation the description of natural facts in which there are never identical cases. Identical cases are created by means of the schematic imitation that we make of reality; and here toe lies the origin of the mutual dependence that appears in the character of facts. To this therefore he restricts the significance of the principle of causality, for which (in order to avoid fancifulness and mythologicism) it would be opportune to substitute the concept of _function._ Bodies or things are abbreviated intellectual _symbols_ of groups of sensations; symbols, that is to say, which have no existence outside our intellect. They are cards, like those which dealers attach to boxes and which have no value except in so far as there are goods of value inside the box. In this economic schematicism lies the strength, but also the weakness, of science; for in the presentation of facts science always sacrifices something of their individuality and real appearance, and does not seek exactness in another way save when obliged to do so, by the requirements of a definite moment. Hence the incongruity between experience and science. Since they are developed