The aim of this paper is to outline how Salomon Maimon (1753-1800), based on a resumption of elements of pre-Kantian philosophy, especially Espinosa and Leibniz, criticizes the Kantian solution to the problem of grounding the objective validity of our knowledge and, within this criticism, explains in an original way how the knowledge is justified. It is an original way because Maimon takes up the demand from the point of view of the infinite, but falls not into the illusions of the transcendental appearance denounced by the Kantian Critique, so that he is at the same time, so to speak, pre- and post-Kantian - something that is expressed by the given characterization by Maimon himself to his “system”: “empirical skepticism, dogmatic rationalism”. It is, therefore, a contribution to the understanding of Maimon's philosophy.