Husserl explicitly discusses outsourcing the mathematical symbol system and algorithm (“the most amazing mental machine”, Hua XII, 350) to actual mechanical machines (Hua XII, 364). Switching external signs for internal signs doesn’t really matter since even our own mental symbol manipulation is “blind” (Hua XII, 357) and “thoughtless” (“gedankenlos”, Hua XII, 251; Hua Mat I, 311). Husserl repeatedly underscores that we often don’t even notice the fact that we are actually using signs instead: the use of signs arises naturally and spontaneously. Once we have established the foundational parallelism between proper and improper presentations, we can rely on the algorithm to carry us beyond our contingent psychological limits: “Symbols are the great natural instrument by which the limits of our psychical life, originally so narrow, are broken through” (Hua CW V, 29). Mechanical symbol manipulation replaces mental labor, saving us a lot of time and effort (Hua XXI, 29; Hua XII, 236). This is an enormous cognitive advantage and serves as a force-multiplier for the human mind. Many scientific discoveries would have been totally impossible without the use of symbolic technologies for mechanical calculation and computation.

In his works throughout the 1880s and 1890s, in the Prolegomena, and up to the Crisis, Husserl explicitly connects the use of mechanical tools for thought and our scientific and technological achievements. Likewise the issue of founding, clarifying, and justifying the use of symbol systems (whether mental or mechanical), remains a central topic from the beginnings of Husserl’s philosophy through to its very end. Husserl starts by adopting and adapting the Brentanist philosophy of mathematics: mathematics and symbolic methods are indispensable for science. Symbolic intentionality and symbolic technologies pervade nearly all aspects of our mental life and scientific practice. This seems not only possible and useful, but even necessary. Besides Husserl also others in the School of Brentano, like Ehrenfels, were concerned with the consequences of outsourcing mechanical symbol manipulation: if we can do complex mathematics only thanks to our tools, what does this mean for the status of mathematics as analytic, deductive, and a priori? What changes if we have to use memory aides (“Hülfsmittel für das Gedächtniss”, Ehrenfels 1891, 326) or outsource our cognitive labor to machines, acknowledging their results as correct, while we never carried out any deductions ourselves (Ehrenfels 1891, 329)? How can we rely on the (mental) labor done by (or made superfluous by) mechanical devices? What would justify this? The question of “Justifying Mechanical Calculation” is then addressed in the next section of my article.