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.

Weak though these constraints may be, the capacity of human and institutional agents to satisfy them is severely limited. Principles of rationality are ill suited for the prediction and explanation of human behavior. Nor can they be regarded as prescriptions which rational agents are obliged to obey to the letter. The reason is the same in both cases. Persons, institutions and other alleged specimens of rational agency lack the emotional or institutional stability, the memory and computational capacity and the freedom from self deceit required to satisfy the demands of even weak principles of coherence in belief, value and choice. Our rationality is severely ‘bounded’.

In some respects, beliefs, value judgements and other so-called propositional attitudes relevant to deliberation and inquiry resemble religious vows. Just as religious vows often incur obligations only an angel could fulfil, so too, only a rational angel can satisfy the requirements imposed on rational belief, value and choice.