In his work on the foundations of mathematics, Frege placed the problem in a wider context, namely that of science; the ontological status of thought as the carrier of truthfulness became for him the most important issue. The objectivity of truth and thought seems to require the existence of other people, which consequently requires the existence of the world. Thus, the polemics with epistemological idealism became a key issue for Frege; the topic appears in such works as The Basic Laws of Arithmetic, The Logic, and The Thought. What seems to be most interesting in Frege’s work is his stress on weaknesses of both epistemological realism and immanent idealism. Reflecting upon the examples of the physiological psychology and physiology of the...