In epistemology there is a tension between considering what people believe and know, and prescribing acceptable ways of believing and knowing. This tension is understandable; after all, an epistemologist, given that he is not a complete sceptic, can hardly avoid taking note of the fact that we actually do know and believe certain things, as well as taking account of what we know, and of how we know, or at least claim to know. This is most obviously true in the case of natural science, where it would be folly not to take account of scientific success and progress, and not to record that those who have achieved this success cannot have been following a wholly mistaken method of acquiring beliefs. But what is true of science is true of other more mundane perceptions and beliefs with which scientific beliefs are sometimes continuous.

At the same time it cannot be the task of the epistemologist merely to codify practice. The history and sociology of knowledge and belief must not be confused with the critical, reflective task of the philosopher. It is also the epistemologist's task to reflect on what ought to be the case, on how epistemic endeavours ought to be prosecuted, on tools and methods and standards. Much of what appears at first sight to be descriptive and reportive in the work of epistemologists turns out, on closer inspection, to be prescriptive and recommendatory. This study is a contribution to epistemology of such an overtly prescriptive kind.

Many reasons are given for adopting and abandoning beliefs, reasons to do with personal well-being, with the achieving of power, success, freedom from temptation, and much else.