Franz Brentano is one of the major figures of what is known as the “Austro-German” tradition. A distinctive feature of this tradition is its concern with clarity and argument, as opposed to the speculative and “jargon-laden” philosophy of the nineteenth century, which is to say—according to the Austro-German authors themselves—post-Kantian idealism. In this respect, the Austrian philosopher and Catholic priest Bernard Bolzano, inasmuch as he was anti-Kantian and anti-idealist, can be placed at the origins of Austro-German philosophy. It should be noted that Bolzano was well-versed in Aristotelian philosophy and logic, as the numerous references in his Wissenschaftslehre of 1837 attest. Nonetheless, the most influential thinker in the Austro-German tradition was not Bolzano, but Brentano. From a methodological perspective, Brentano also insists on the importance of clarity and argument, and he also is opposed to speculative thinking. In the famous fourth thesis in his Habilitationsschrift, he maintains that philosophy, which includes psychology, should follow “the method of the natural sciences,” that is, it should be based on experience. In the case of psychology, this amounts to saying that it must rest on “inner perception”—in other words, it should be done from the point of view of reflexive consciousness—and free itself from any metaphysical prejudices. Brentano’s research inspired a large number of followers: probably the best-known products of the school of Brentano are Husserl’s phenomenology, Meinong’s theory of objects, the Lvov–Warsaw school of logic founded by Twardowski, and the various traditions of Gestalt psychology. Brentano himself was a student of Adolf Trendelenburg in Berlin. Trendelenburg played an important role in the renewal of Aristotelian thought in the German-speaking world: he taught the philosophy of Aristotle for almost thirty years without interruption, and was a major influence on many students. Having in this way become familiarized with the philosophy and psychology of Aristotle, Brentano wrote his famous doctoral thesis on the Aristotelian theory of categories in 1862, and his Habilitationsschrift on Aristotles’s psychology in 1867. These two works also attach great importance to the scholastic reception of Aristotle’s philosophy, especially Thomas Aquinas. This interest in Aristotle was not confined to Brentano’s youth: he published books on Aristotle throughout his life, and regularly lectured on the history of ancient and medieval philosophy. It should also be pointed out that Brentano too was a priest, but left the priesthood around 1870 after contesting the doctrine of papal infallibility.