Reliabilism
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). The most popular form of reliabilism is process reliabilism.
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 reliablist 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', one must be justified in believing that p in order for that belief to constitute knowledge; the traditional analysis has it that knowledge is no more than justified true belief. 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 a form of epistemic externalism. Another objection to reliabilism is the new evil demon problem.
Another of the most common objections to reliabilism, made first to Goldman's reliable process theory of knowledge and later to other reliabilist theories, is the so-called generality problem, as follows. For any given justified belief (or instance of knowledge), one can easily identify many different (concurrently operating) "processes" from which the belief results. My belief that there is a bird in the tree outside my window might be accorded a result of the process of forming beliefs on the basis of sense-perception, of visual sense-perception, of visual sense-perception through non-opaque surfaces in daylight, and so forth, down to a variety of different very specifically-described processes. Some of these processes might be statistically reliable, while others might not. It would no doubt be better to say, in any case, that we are choosing not which process to say resulted in the belief, but instead how to describe the process, out of the many different levels of generality on which it can be accurately described.