have carried it to its ultimate elements. (C.S. Peirce, "Letters to Lady Welby" (14 December 1908), Selected Writings, pp. 396–397). See also Bradley's regress Unity of the proposition References Peirce, C.S., "Letters to Lady Welby", pp. 380–432 in Charles S. Peirce: Selected Writings (Values in a Universe of Chance), Philip P. Wiener (ed.), Dover, New York, NY, 1966. Abstraction Mathematical logic Charles Sanders Peirce