The article focuses on the concept of reasonableness as described by American philosopher Charles S. Peirce in his writings dating between 1899 and 1908. Peirce's writings considered by the author are found in the books "Contributions to The Nation," vols. 1-4, edited by K. L. Ketner and J. E. Cook, and "Collected Papers of Charles Sanders Peirce," vols. 1-8, edited by C. Hartshorne, P. Weiss and A. W. Burks. The author considers 20th century Western philosophies of reason, pragmatism, scientism, thirdness, postmodernism, and philosopher Walker Percy's criticisms of Peirce's arguments regarding reasonableness.