Epistemology

Epistemology is the area of philosophy that is concerned with knowledge. It is concerned with the sources of knowledge (innate ideas, experience, etc.), the nature of knowing and the limits of knowledge. Epistemology considers that knowledge can be obtained through empiricism and/or rationalism.

Sources of Knowledge

There are five major sources of knowledge:

1. Perception — that which can be perceived through the experiences of the senses.
2. Introspection — knowledge of one's self that can be found through internal self-evalution. (For example, I know I am hungry or tired.)
3. Memory — Memory is the storage of knowledge that was learned in the past — whether it be past events or current information.
4. Reason — Reason can be considered a source of knowledge a priori, meaning prior to experience. One can assume, for example, that all humans are mammals, through the use of reason. It is not neccessary to observe every human to arrive at this conclusion. In the same way, one can know that 500 plus 2 is 502, without actually counting five-hundred items, adding two, and then counting them again.
5. Testimony — Unlike other sources of knowledge, testimony relies on others to acquire knowledge and communicate it to us.

It is important to note that at least four these sources are fallible. Perceptions may be flawed, as one may interperet the senses incorrectly and arrive at the wrong conclusion (consider optical illusions as an example). Introspection may be flawed by mistaken feelings or emotions. Memories can be confused, faded or forgotten. Testimony can be false, or come from unreliable sources. (Some even argue that Testimony is a source of belief or supposition, not of knowledge.

Reason, too, can be fallible, when human error is considered. However, if all reason is conducted properly, then, in theory, all a priori knowledge should be true. Some epistemologists, however, argue that reason is not a true source of knowledge, but that these things are learned from experience (empiricism).