Epistemology
Epistemology deals with questions like "What is knowledge?" and "How do we know this?".
Etymology
"Epistemology" from "ἐπιστήμη" (knowledge) and "λόγος" (logos) was introduced into English by the Scottish philosopher James Frederick Ferrier.
Hellenistic views
The questions are as old as Philosophy itself, and the search for answers continues today.
Plato viewed knowledge as universal unchanging Ideas. One dialogue shows how all knowledge is inherent in everyone, whereas another says that that which must be there already to be able to percieve the world around him.
Aristotle tried to divide the types of knowledge, that which can be said of knowledge, into ten Categories. He further attempts to classify knowledge in books named physics, metaphysics, poetry (including theater), biology and zoology, logic, rhetoric, politics, government, and ethics. These areas of knowledge retain his names today.
Scientific revolution: reason and experiment
Reason and observation are important for knowledge to all philosophers, but are viewed differently from different vantage points.
Empiricims
Empiricists, like John Locke later stresses the importance of observation and experiments to obtain knowledge, even to the point of assuming that a new born child has a tabula rasa.
Ratonalism
Rationalists like René Descartes stress reason to arrive at knowledge since one can not always trust the senses.
Modern
Immanuel Kant tries to resolve many issues, uses his twelve categories of knowledge and argues, as Plato did before, that there has to be something in man already there to let observation into the mind. That which is already there before is a priori and gives a rational basis for handling the empirical knowledge, which is a posteriori knowledge.