The idea behind the book is to provide a comprehensive analysis of the development of Husserl’s earliest philosophy, from his 1887 Habilitation essay up to and including his first book, the 1891 Philosophy of Arithmetic.

In the book, I provide a reconstruction of his habilitation essay, something no-one has ever tried before. This may be due to the fact that there is a lot of confusion surrounding this work. What we still have today is only the first chapter of the habilitation essay, which was printed, but not actually sold in stores. This first chapter is known by the same title as the habilitation essay: Über den Begriff der Zahl. Psychologische Analysen. But they are not the same thing, not by a long shot. This partial print was then re-published in Husserliana XII under the very misleading title “Original version of the first four chapters [of the Philosophy of Arithmetic]”. The sources I take into consideration clearly show that the original version of the habilitaiton essay was by far broader than the printed version, including topics from the very last chapters of the Philosophy of Arithmetic.

Thanks to this reconstruction, I can show and analyze the changes in Husserl’s position between 1887 and 1891, which can tell us a great deal about the influences on Husserl in this period. In the book I concentrate mostly on his mathematical background (mainly Weierstrass, Kronecker) and the context of the School of Brentano (mainly Brentano, Stumpf, Meinong), but I will also try to include a chapter on Frege, since I think that my reconstruction allows to shed more light on the issue of Frege’s influence on Husserl.

Besides all this, I am including the notes of Brentano’s logic lectures taken by Eduard Leisching (an uncle of Ludwig Landgrebe, who was assistant of Husserl and later worked at the Husserl-Archives) as an appendix. These are especially interesting for the development of Husserl’s early position, because they record the lectures that Husserl himself attended in the winter semester 1884/1885: these are the lectures that gave the breakthrough for Husserl to dedicate himself wholly to philosophy under Brentano’s direction.