Are you sure twice two are four? Not at all. A certain percentage of the human race are insane and subject to illusions. It may be you are one of the… - Charles Sanders Peirce

The Scientific Attitude and Fallibilism in Philosophical Writings of Peirce, selected and edited with an introducton by Justus Buchler. p. 49

It has never been in my power to study anything, — mathematics, ethics, metaphysics, gravitation, thermodynamics, optics, chemistry, comparative anatomy, astronomy, psychology, phonetics, economics, the history of science, whist, men and women, wine, metrology, except as a study of semeiotic.

The third category of which I come now to speak is precisely that whose reality is denied by nominalism. For although nominalism is not credited with any extraordinarily lofty appreciation of the powers of the human soul, yet it attributes to it a power of originating a kind of ideas the like of which Omnipotence has failed to create as real objects, and those general conceptions which men will never cease to consider the glory of the human intellect must, according to any consistent nominalism, be entirely wanting in the mind of Deity.