A striking passage from Frege’s unpublished essay “Boole’s logical calculus and the concept-script,” which he submitted in 1881 first to Zeitschrift für Mathematik und Physik, then the Mathematischen Annalen, and finally the Zeitschrift für Philosophie und philophische Kritik, but was rejected each time:
I now return once more to the examples mentioned earlier, so as to point out the sort of concept formation that is to be seen in those accounts. The fourth example gives us the concept of a multiple of 4 […]. The eighth example gives us the concept of the congruence of two numbers with respect to a modulus, the 13th that of the continuity of a function at a point etc. All these concepts have been developed in science and have proved their fruitfulness. For this reason what we may discover in them has a far higher claim on our attention than anything that our everyday trains of thought might offer. For fruitfulness is the acid test of concepts, and scientific workshops the true field of study for logic.
This is pp. 32-33 in the translation by Peter Long and Roger White, with the assistance of Raymond Hargreaves, in Posthumous Writings, edited by Hans Hermes et al (Blackwell, 1979).
This remains one of the lesser appreciated themes in Frege’s work. The standard fare in a philosophy major mentions sense and reference, concept and anti-psychologism, but I’d bet even very few working philosophers are familiar with these suggestive passages on fruitfulness. Of course, every time I read the word I can only think of Keats, on autumn: “Season of mists and mellow fruitfulness…”
Some helpful discussions appear in:
- Jamie Tappenden, “Fruitfulness as a Theme in the Philosophy of Mathematics,” The Journal of Philosophy (2012)
- Jamie Tappenden, “The Mathematical and Logical Background to Analytic Philosophy,” The Oxford Handbook of the History of Analytic Philosophy
- Jamie Tappenden, “Extending knowledge and ‘fruitful concepts’: Fregean themes in the philosophy of mathematics,” in Gottlob Frege: Critical Assessments of Leading Philosophers, Vol. III, Frege’s philosophy of mathematics, edited by Michael Beany and Erich Reck