Scepticism, Certainty, and Defeasibility

In a first analysis, the ‘Cartesian’ argument denying the possibility of perceptual knowledge is compared with acceptable and unacceptable arguments that occur in non-philosophical contexts. Its illusory force is attributed to similarities to the former, its invalidity to differences partly shared with the latter. A variety of possible moves in defence of scepticism are then critically considered. Discussion of a confusion between infallibility and certainty leads into the topic of probability and a critique of two related responses to scepticism, ‘fallibilism’ and ‘contextualism’, that discard the intuitive link between knowledge and objective certainty. The argument calls on the notion of ‘defeasibility’, a term imported from jurisprudence into epistemology (where it is seriously ambiguous—see Chapter 6). Its relation to the notion of burden of proof and to argumentation theory is explained, and a particular sense is accordingly proposed in which ascriptions of knowledge may be both certain and ‘defeasible’.