 We invoke our illustrious forebears here mainly to illustrate the great scope of their ambitions, with the hope that their meliorist spirit will breathe life into the material covered in this article. In the midst of mathematical detail, it is easy to forget that formal epistemology is an expression of the hope that reason can be productively turned upon itself. If this project is miscarried, we risk obstructing or artificially circumscribing the scope and power of human reason. But what if it succeeds? 