This is the the tenth post in my Theories of Knowledge and Reality series. Follow the link for more on the series and for links to other entries as they appear.
Reliabilism responds to skepticism by challenging one of Descartes' key methodological assumptions. He claims that you can't know anything unless you have absolute certainty of that thing, not just having a subjective sense of feeling certain but an absolute, objective understanding of why that thing must be true. No one, of course, has such certainty about most things we believe. Reliabilists just argue that we don't need to. Knowledge just doesn't involve that kind of certainty. Reliabilists simply deny the premise that everyone else seems to assume, that knowledge requires this idea of absolute certainty. Reliabilists consider such a notion ridiculous.
We know all sorts of things without being able to prove them to ourselves and without being able to rule out all the alternatives. How do we ordinarily use the word 'know'? We say we know all sorts of things. How do we find out what words generally mean? We see how people use them. In this case, people use the word 'know' when they don't have certainty.