The paper argues that Brentano was the exponent of a methodological monism, which is based on the requirement that science should be grounded on experience, and not on a speculative-idealistic principle, as in the case of German idealism. In Brentano’s psychological writings, this methodological requirement concretized in two different theses: (T1) The method of psychology is identical with the method of natural science; (T2) The method of psychology is inspired by the method of natural science. The thesis of this study (...) is that an important part of Psychology from an Empirical Standpoint is elaborated in accordance with T1. By contrast, Brentano’s Descriptive Psychology illustrates the subsequent decision to give up this idea. In its place, the aforementioned requirement is elaborated in the spirit of a methodological particularism that recommends the scientist elaborate his methods according to the specificity of the phenomena under investigation and to the difficulties that need to be overcome when approaching them. (shrink)