Already in ancient Greece the importance of mathematical and logical thinking for philosophy was widely recognized, especially in the schools of the two giants Plato and Aristotle. With the explosive development of logic in the last decades of the nineteenth century, mostly in the hands of Gottlob Frege, and the parallel development of mathematics beginning already in the first decades of that same century with the discovery of non-Euclidean geometries, continuing with the arithmetization of analysis, the emancipation of abstract algebraic structures and Riemann’s theory of manifolds, and culminating with the birth of topology and of Cantor’s set theory, it became perfectly clear for the best philosophical minds not only that they could not ignore the extraordinary developments in the two sister disciplines, and in some cases even that they should make use of some logical and mathematical tools in their philosophical endeavours.