Epistemology, the study of the theory of knowledge, is among the most important areas of philosophy. The questions that it addresses include the following:

What is knowledge?

The first problem encountered in epistemology is that of defining knowledge. Much of the time, philosophers use the tripartite theory of knowledge, which analyses knowledge as justified true belief, as a working model. The tripartite theory has, however, been refuted: Gettier cases show that some justified true beliefs do not constitute knowledge. Rival analyses of knowledge have been proposed, but there is as yet no consensus on what knowledge is. This fundamental question of epistemology remains unsolved.

Though philosophers are unable to provide a generally accepted analysis of knowledge, we all understand roughly what we are talking about when we use words such as “knowledge”. Thankfully, this means that it is possible to get on with epistemology, leaving unsolved the fundamental question as to what knowledge is.

From where do we get our knowledge?

A second important issue in epistemology concerns the ultimate source of our knowledge. There are two traditions: empiricism, which holds that our knowledge is primarily based in experience, and rationalism, which holds that our knowledge is primarily based in reason. Although the modern scientific worldview borrows heavily from empiricism, there are reasons for thinking that a synthesis of the two traditions is more plausible than either of them individually.

How are our beliefs justified?

There are better and worse ways to form beliefs. In general terms, it is important to consider evidence when deciding what to believe, because by doing so we are more likely to form beliefs that are true. Precisely how this should work, when we are justified in believing something and when we are not, is another topic in the theory of knowledge. The three most prominent theories of epistemic justification are foundationalism, coherentism, and reliabilism.

How do we perceive the world around us?

Much of our knowledge, it seems, does come to us through our senses, through perception. Perception, though, is a complex process. The way that we experience the world may be determined in part by the world, but it is also determined in part by us. We do not passively receive information through our senses; arguably, we contribute just as much to our experiences as do the objects that they are experiences of. How we are to understand the process of perception, and how this should effect our understanding of the world that we inhabit, is therefore vital for epistemology.

Do we know anything at all?

The area of epistemology that has captured most imaginations is philosophical scepticism. Alongside the questions of what knowledge is and how we come to acquire it is the question whether we do in fact know anything at all. There is a long philosophical tradition that says that we do not, and the arguments in support of this position, though resisted by most, are remarkably difficult to refute. The most persistent problem in the theory of knowledge is not what knowledge is or what it comes from, but whether there is any such thing at all.