 Cohen’s colleague at Marburg, Natorp, would emphasize a major advantage of the transcendental method for Cohen (Natorp 1912, 196–7). This method allows Cohen to avoid what he and his students took to be the two major errors of other post-Kantian philosophy. First, because Cohen sought to explain the possibility of experience by appeal to a priori laws in it, he avoided the physiologically-oriented psychologism of Helmholtz and Lange, among others. But second, the transcendental method anchors Kantian philosophy to mathematical natural science as its starting point. This anchor prevents philosophy from taking off on the speculative, metaphysical flights of fancy that, in the minds of many Kantian philosophers in the 1860s and 1870s, decisively undermined the Idealist Naturphilosophie of the first half of the nineteenth century. For Cohen and his students, the transcendental method thus makes possible a philosophy that is properly scientific, without absorbing it completely into physiology and psychology.