The epistemo-methodological prerequisites for comparing mainstream and formal epistemologies concentrate on the following items: the modality of knowledge, infallibility, forcing and the reply to skepticism; the interaction between epistemology and methodology; the strength and validity of knowledge; reliability; and the distinction between a first-person perspective and a third-person perspective on inquiry.

Modal Knowledge, Infallibility and Forcing

Agents inquire to replace ignorance with knowledge. Knowledge is a kind of epistemic commitment or attitude held toward propositions or hypotheses describing some aspect of the world under consideration. Agents may in general hold a host of different propositional attitudes, such as belief, hope, wish, desire etc. But there is a special property that knowledge enjoys over and above the other commitments. As Plato pointed out, a distinct property of knowledge is truth. Whatever is known must be true; otherwise it is not knowledge, even though it very well may qualify as belief or some other propositional attitude.

Contemporary notions of knowledge are often modal in nature. Knowledge is defined with respect to other possible states of affairs besides the actual state of affairs (Fig. 2.1). The possibility of knowledge seems ruled out when it is possible that we err. Introducing other possible state of affairs is an attempt to preclude exactly these error possibilities. Knowledge must be infallible by definition. As Lewis (1996) puts it, “To speak of fallible knowledge, of knowledge despite uneliminated possibilities of error, just sounds like a contradiction” (p. 367).