The purpose of this paper is to show peirce's critical attitude toward two basic elements in the positivistic view of human knowledge, sensation and hypothesis. by 'positivism' i mean the nineteenth-century brand, this is the version peirce knew and attacked. the logic of the paper is simple. i state the positivistic position as found in the writings of comte, pearson, mach and poincare. i follow with peirce's criticism in the light of his realistic view of sensation and his belief that (...) hypothesis or abduction is a valid form of inference. (shrink)