 A central principle of Brentano’s philosophy, which should become widely accepted among Brentano’s students, was that philosophy should be done in a rigorous, scientific manner. Already early in his career, in the public defense of his Habilitation in 1866, he stated 25 theses, the fourth of which reads: “The true method of philosophy is that of natural science.” (contained in: ZP, 136, my translation) [“Verae philosophiae methodus nihil alia est nisi scientiae naturarum”]. Brentano, thus, opposed the idea that there was a unique method for philosophy and denied that there was a “first philosophy” that could unveil genuinely philosophical truths and thus play a privileged or foundational role in the overall system of the sciences. According to Brentano, philosophy—and in particular philosophical psychology—should apply a method that is based on observation, description of facts, and induction; just like the (other) natural sciences.