Epistemology is a much abused word. In philosophy, it refers to the sub-discipline concerned with the justification of beliefs. Epistemology is about a) the formal problem of how beliefs are justified in general and b) how justified you might be in holding a specific belief. This is quite a straightforward procedure: it involves defining what we might accept to constitute 'evidence' and how evidence relates to beliefs, and applying that to specific situations. For instance, we might ask whether hearsay constitutes valid evidence, or whether experiment is the criterion of justification, and then we could say whether or not I am justified in believing that water is potable or that I speak English. Pretty simple. Of course, we then have to justify why it is that we have adopted these criteria for establishing what is and what is not evidence, and so the criteria for that have to established as well - resulting in a fairly complex argument about the nature of justification (and a fair number of '-isms', confusing for the neophyte). Epistemology in this sense takes it for granted that you can know things, and it concerns itself primarily with how people know things and how justified they are in knowing them under certain conditions.
In 'critical theory', however, epistemology can mean something entirely different. It tends to refer to a priori judgements, prior beliefs, and worldview - the things that make it impossible for you to truly know things. Different theoretical positions are called 'different epistemologies', even if they take the same track with regard to the formal justification of beliefs. Science is considered simply one epistemology, or 'way of knowing', as opposed to the attempt to find out about the world, and it is therefore held to have no authority over what constitutes a justified belief about the world. This is a very strange view, but it has more-or-less taken over in some parts of the social sciences. It rests on the view that all beliefs have to be self-supporting or are only supported within a scheme of thought that cannot itself be taken for granted, depending solely on cultural foundations. This is itself not a justifiable position, but its supporters deem that okay, as the idea that it is not justifiable is a judgement from a particular school of thought, and can be ignored (combining this view with the genetic fallacy, the view that arguments are wrong depending on their origins; argumentum ad Hitlerum is a good example of the genetic fallacy). This makes it both pernicious and stupid.
Epistemology is also regularly confused with ontology, another of English's most abused words, but to unravel that stupid continental mess would take another article on its own, and so I won't bother here. Suffice it to say that epistemology means something entirely different within the 'critical theory' echo chamber from its usage without. This 'critical theory' view would say that no beliefs are justified except within their own sphere of reference - that the belief that water consists of one oxygen and two hydrogen atoms joined by covalent bonds is only 'justified', if at all, within the science epistemology, and doesn't have any independent validity. Another person's beliefs about water - say, that it is hot and dry and consists of extremely fine particles of sand - are equally justified within the person's own epistemology, in this view.
Discussion of formal epistemology is quite boring, and it shouldn't really have a place in the social sciences. It's the philosopher's job to deal in it, and they deal in it rather well. But as social science is infested with people who believe that different cultures have different epistemologies, none superior to the other, all of them socially- and culturally-determined, it seems to be necessary to delve into epistemology now and then. I've made a concerted effort to do this, and it has involved a considerable amount of frankly boring reading. But I believe it is important to know whether you have a leg to stand on in a debate, and the debate about whether science works or whether we are justified in believing things about the world independently of our social or cultural backgrounds is important in itself, especially so given the challenges offered by 'critical theory' types without a single truly critical bone in their bodies.
I'm going to post some things about epistemology over the next few weeks. I'll start off with a post about foundationalism, coherentism, and foundherentism - three approaches to the formal justification of belief. I'll try to make this as painless as possible. I'll then try to get onto how ontology relates to epistemology, because this is not a trivial relationship. I want to look as well at how beliefs are justified in real scientific inquiries, and so I'll try to use some good archaeological materials to show how this works. I'll relate the whole discussion to the social sciences, especially archaeology and social anthropology, two of the disciplines most plagued by knowledge-deniers. Hopefully, this will provide a way for 'critical theory' people to see just why it is that I and others disagree with them and their precepts, and why the fight for good sense and critical thinking (truly critical thinking) in arch & anth is a) important and b) founded on a firm philosophical basis.
'Critical theorists' like to believe that they are the philosophically-sophisticated ones - that people who don't endorse 'post-isms' are rubes living in the nineteenth century, probably with a racist or pro-colonial axe to grind. In reality, they are the ones who have left good sense behind and have bought into some very silly principles, and it is only right that they be made aware of this.