After barely two weeks of doing research at the Houghton Library in Harvard, I can already report a major new discovery among the manuscripts of Franz Brentano. Within the folder holding his early correspondence with Edmund Husserl, I found a letter from Husserl to Brentano from 29 December 1889 that is not mentioned anywhere in Schuhmann’s Husserl-Chronik, nor does it appear in the Briefwechsel, the official edition of Husserl’s correspondence. Thomas Vongehr from the Husserl-Archives Leuven and Robin Rollinger have independently confirmed that this is indeed a new and unknown letter. The letter can be found in the Houghton collection of Brentano’s correspondence (call number “MS Ger 202”), as manuscript 2074, pages 1 through 6. I have already made a preliminary transcription and translation, and am planning to publish it as soon as possible.

At the beginning of the letter Husserl spends some obligatory paragraphs thanking Brentano and congratulating him for the recent publication of his work “Vom Ursprung sittlicher Erkenntnis” (“On the Origin of Moral Knowledge”). He then apologizes for not having written earlier, due to an illness, from which he eventually recovered during a holiday in the Alps. More importantly, Husserl proceeds to discuss having taken up again his work on the philosophy of mathematics (i.e. the Philosophy of Arithmetic) that he had already begun in Vienna. He unambiguously states that he was essentially inspired by Brentano’s logic lectures from the WS 1885/86 and that he ran into trouble with the logical character of universal arithmetic: the concept of amount (Anzahl) and the doctrine of improper presenting were not sufficient to tackle these problems. Now, Husserl affirms, he has overcome these difficulties and feels ready to deal with the remaining issues. These include the foundations of geometry and the theory of the continuum, about which he indeed had begun to write already during his studies with Brentano and were meant at first as the main topic for his Habilitation (see the manuscript “Homogene und Inhomogene Continua” (K I 50/47) and Brentano’s letter to Stumpf from 18-10-1886).