Reliabilism, a category of theories in the philosophical discipline of epistemology, has been advanced both as a theory of knowledge and of justified belief (as well as other varieties of so-called positive epistemic status). Process reliabilism has been used as an argument against philosophical skepticism, like the brain in a vat idea. Process reliabilism is a form of epistemic externalism, and is quite popular.
As a theory of knowledge, reliabilism can be roughly stated as follows:
One knows that p (p stands for any proposition--e.g., that the sky is blue) if and only if p is true, one believes that p is true, and one has arrived at the belief that p through some reliable process.
As a theory of justified belief, reliabilism can be formulated roughly as follows:
One has a justified belief that p if, and only if, the belief is the result of a reliable process.
Moreover, a similar account can be given (and an elaborate version of this has been given by Alvin Plantinga) for such notions as 'warranted belief' or 'epistemically rational belief'.
Leading proponents of reliabilist theories of knowledge and justification have included Alvin Goldman, Marshall Swain, and more recently, Alvin Plantinga. Goldman's article "A Causal Theory of Knowing" (Journal of Philosophy, v. 64 (1967), pp. 357–372) is generally credited as being the first full treatment of the theory, though D. M. Armstrong is also regarded as an important source, and (according to Hugh Mellor) Frank Ramsey was the very first to state the theory, albeit in passing.
On the classical or traditional analysis of 'knowledge' is justified true belief justified true belief(JTB). In order to have a valid claim of knowledge for any proposition, one must be justified in believing "p" and "p" must be true. Since Gettier proposed his counterexamples the traditional analysis has included the further claim that knowledge must be more than JTB. Reliabilist theories of knowledge are sometimes presented as an alternative to that theory: rather than justification, all that is required is that the belief be the product of a reliable process. But reliabilism need not be regarded as an alternative, but instead as a further explication of the traditional analysis. On this view, those who offer reliabilist theories of justification further analyze the 'justification' part of the traditional analysis of 'knowledge' in terms of reliable processes. Not all reliabilists agree with such accounts of justification, but some do.
Objections to the Theory
Some find reliabilism of justification objectionable because it entails externalism, which is the view that one can have knowledge, or have a justified belief, despite not knowing (having "access" to) the evidence, or other circumstances, that make the belief justified. Most reliabilists maintain that a belief can be justified, or can constitute knowledge, even if the believer does not know about or understand the process that makes the belief reliable. In defending this view, reliabilists (and externalists generally) are apt to point to examples from simple acts of perception: if one sees a bird in the tree outside his window and thereby gains the belief that there is a bird in that tree, he might not at all understand the cognitive processes that account for his successful act of perception; nevertheless, it is the fact that the processes worked reliably that accounts for why his belief is justified. In short, he finds he holds a belief about the bird, and that belief is justified if any is, but he is not acquainted at all with the processes that led to the belief that justified him in having it. Of course, internalists do not let the debate rest there; see externalism (epistemology).
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