In my VENI project description I included a “background” section in which I tried to explain who Brentano and his students were ad why their approach to the issue of philosophy as science was important. It is written, like most of the project proposal, with a general humanities committee in mind, so not for specialists in the history of 19th century philosophy.
Franz Brentano (1838–1917) is probably best known for re-introducing the concept of intentionality in philosophy: that all mental acts (believing, fearing, willing, etc.) are directed at something or have something as content (Brentano 1874, 124). Brentano began to attract students such as Carl Stumpf and Anton Marty to his cause after defending his habilitation theses in Würzburg in 1866. His notoriety increased with his Psychology from the Empirical Standpoint (Brentano 1874) and his lectures in Vienna (1874-1895) which influenced i.a. Alexius Meinong, Christian von Ehrenfels, Edmund Husserl, and Kazimierz Twardowski.
The scientific status of philosophy became a mainstream issue at first in 19th century philosophy. Against the complex background of the progress and specialization of the natural sciences as well as the growth and professionalization of universities, Brentano advanced his ideal of philosophy as science in his famous fourth habilitation thesis: “The true method of philosophy is none other than that of the natural sciences” (Brentano 1929, 136-7). Brentano argued that philosophy is not done by grandiose speculation, but by humble, detailed investigation. “We are taking the first steps towards the renewal of philosophy as science” he told his students, not by building up “proud systems”, but by humbly “cultivating fallow scientific ground” (Brentano 1929, 131).
The 19th century idea of collaborative research led to a division of labor in Brentano’s school. Each of his students worked out a part of the greater whole: Stumpf, the philosophy of sound; Marty, language; Meinong the history of philosophy; Husserl, mathematics; etc. Yet they were also concerned with the renewal of philosophy as science and, besides their work in epistemology, logic, and philosophy of science, they discussed the scientific status of philosophy and its relation to other sciences in programmatic works (e.g. Stumpf 1907, 1908; Meinong 1907; Husserl 1911).