This paper discusses the function of principles of rationality in inquiry and deliberation rather than the content of such principles. Appealing to the belief-doubt model of inquiry pioneered by C. S. Peirce and J. Dewey, I shall argue that principles of rationality should impose weak constraints on the coherence of the beliefs, values and choices of deliberating and inquiring agents. Efforts to derive substantial moral or theoretical deliverances from such principles are, thereby, ruled out of court.