Internalism and externalism in epistemology

The internalism–externalism distinction is usually applied to the epistemic justification of belief. The most common form of internalism (accessibility internalism) holds that only what the subject can easily become aware of (by reflection, for example) can have a bearing on justification. We may think of externalism as simply the denial of this constraint.

The strong intuitive appeal of internalism is due to the sense that we should be able to determine whether we are justified in believing something just by carefully considering the question, without the need for any further investigation. Then there is the idea that we can successfully reply to sceptical doubts about the possibility of knowledge or justified beliefs only if we can determine the epistemic status of our beliefs without presupposing anything about which sceptical doubts could be raised – the external world for example.

The main objections to internalism are: (1) It assumes an unrealistic confidence in the efficacy of armchair reflection, which is often not up to surveying our entire repertoire of beliefs and other possible grounds of belief and determining the extent to which they support a given belief. (2) If we confine ourselves to what we can ascertain on reflection, there is no guarantee that the beliefs that are thus approved as justified are likely to be true. And the truth-promoting character of justification is the main source of its value.

Externalism lifts this accessibility constraint, but in its most general sense it embodies no particular positive view. The most common way of further specifying externalism is reliabilism, the view that a belief is justified if and only if it was produced and/or sustained by a reliable process, one that would produce mostly true beliefs in the long run. This is a form of externalism because whether a particular belief-forming process is reliable is not something we can ascertain just on reflection. The main objections to externalism draw on internalist intuitions: (1) If the world were governed by an evil demon who sees to it that our beliefs are generally false, even though we have the kind of bases for them we do in fact have, then our beliefs would still be justified, even though formed unreliably. (2) If a reliable clairvoyant (ones who ‘sees’ things at a great distance) forms beliefs on this basis without having any reason for thinking that they are reliably formed, those beliefs would not be justified, even though they pass the reliability test.