Earlier this year I discovered an unknown letter from Husserl to Brentano from 29 December 1889 at the Houghton Library in Harvard among Brentano’s correspondence (Franz Clemens Brentano Correspondence, 1867-1917 (MS Ger 202). Houghton Library, Harvard University, number 2074, pp. 1-6). The letter has now been published on-line in Husserl-Studies, together with an english translation and a short introduction.
The letter is of some significance, historically and systematically, for the development of Husserl’s philosophy, painting a vivid picture of his relation and indebtedness to his former teacher. Husserl begins by profusely thanking Brentano and apologizing for not having replied sooner. He then goes on to discuss his work on the philosophy of mathematics that he had already begun while studying with Brentano in Vienna, inspired by his lectures. As in his letter to Stumpf of February 1890, Husserl describes the issues he had encountered during the elaboration of his 1887 habilitation work “On the Concept of Number” into what would become the “Philosophy of Arithmetic”:
“I had great difficulties with the full understanding of the logical character of the system of signs of the arithmetica universalis, with its negative and imaginary, rational and irrational numbers. The matter is not so simple that everything could be completely settled with the concept of amount [Anzahl] and the theory of improper presenting.”
However, Husserl also announces that now he has finally found ‘‘clarity’’ regarding the arithmetica universalis and claims that he expects this newfound understanding to help him in resolving the issues he encountered with the foundations of geometry and the theory of the continuum.
I’d like to thank Robin Rollinger and Thomas Vongehr for their assistance with the translation and edition of the letter and the editors Steven Crowell and Sonja Rinofner-Kreidl for their efficient and helpful handling of the publication process.