1. Definition And Key Questions. Epistemology is the branch of philosophy which studies the nature of knowledge and truth. It comes from the Greek words episteme (knowledge) and logos (theory). Epistemologists explore questions such as the following: What is knowledge? What does it mean for someone to "know" something? How much can we possibly know? What's the difference between belief and knowledge, between knowledge and opinion, between knowledge and faith? How do we know that 2 + 2 = 4 or that the square root of 49 is 7? Says who, or what? Is there an ultimate ground of knowledge, a world of absolutes? Do we know something from reason or from direct observation, or from a little of both? But no one can "observe" 2 + 2 =4, so how do we know that the statement (or formula) is true? What is truth? Is truth absolute or relative? What is the relationship between the observer and the observed, the knower and the known? Is there an external world which we can make meaningful statements about and know? Is an object of knowledge a construction of mind? Is the world my idea of it, as Schopenhauer would say, or does it exist independently of all observers? These are just some of the problems that epistemologists address.
2. Prevailing Views. transcendental Realism. View most famously of Plato. Ground of knowledge and truth is a transcendental world of changeless Forms in which ultimate meaning inheres. To know anything is to apprehend the Form of it. A Form is an archetype on which particulars are patterned; there is a hierarchy of Forms, the highest being the Good. The natural world is fleeting; sensory perception is ever shifting. True knowledge is immutable, static (square root of 49 isn't 7 one day and something else the next), ascertainable not by sensory experience but through reason. Deep knowledge -- e.g., of abstract ideas -- is rare and only attainable by philosophers. Immanent Realism: View propounded most famously by Aristotle. Form inheres in the objects we perceive; it doesn't transcend the material thing. Truth is the correspondence of thought with objective fact. External things are knowable and can be classified and understood. The test of truth is the comparison between the thought and fact: is the fact the same as the thought that thinks it? Rationalism: View of Augustine, Aquinas, Descartes, Spinoza, and Leibnitz inherited from Plato. Things of the world are known through reason and intuition, independently of experience. Reason, depending on the thinker, is inspired and informed by Forms, or by God, or by an innate sense. We understand mathematical truths by means of our reason alone. Rationalists don't deny that the senses provide reports of things; they deny that observation and experiment can lead to direct apprehension of truth. Empiricism: View of Locke, Hume, J.S. Mill, Russell; the school of thought that influenced pragmatism in 19th-century America. Knowledge is derived from experience, either by direct observation (use of sight or hearing or touch or taste) or by experimentation (analyzing something under a microscope, in the lab). Empiricists generally don't deny that reason exists and plays some part in cognition; they simply reject the notion that knowledge can be attained by use of reason. Different schools of empiricism and rationalism exist; some extreme, some more temperate. Agnostic Phenomenalism: View of Immanueal Kant. We can't know things in themselves; the reality transcending consciousness will forever remain unknown to us. We can only know truth in its relation to our mind, or as it appears in the objects of the world. Dualism: View of Locke, Santayana. There's an objective world outside the mind that can be known through representations of it in our mind; examples include sensory data, ideas, and essences. The knower is different from the known. This view is the opposite of monism, which sees the world as one stuff, as knower and known are inextricably a part of the same universal essence and/or process. Scepticism: Uncertainty that anything can be postulated, whether about the world, about morals and values, or anything else. Nihilism: View of Nietzsche. There is no truth, no moral essences, no transcendental world, no God, no knowledge. Facts don't exist; only interpretation. Anything that can be said about knowledge is an interpretation -- no more, no less. Pragmatism: View of C.S. Peirce, William James, and John Dewey. Truth is the effectiveness of an idea used as an hypothesis. Test of truth is whether an idea works when subjected to experiment. Utility and predictive power are two criteria of an idea's truthfulness. Realism: Acceptance of dualism; belief in a knowable external world, the independence of a knower/perceiver, and the realness of everyday experience. Idealism: View of Berkeley, Hegel, Bradley. Knowledge is a process in which limited minds move toward identification with Mind, Spirit, Absolute Idea, or Truth. In all of these schools of thought, there are divisions, idiosyncracies, and internal debates.
Plato: Republic; Phaedo; Theaetetus; Parmenides
Aristotle: Physics; Metaphysics
Aquinas: Summa Theologica
Locke: An Essay Concerning Human Understanding
Hume: An Enquiry Concerning Human Understanding
Kant: Critique of Pure Reason; Critique of Practical Reason
J.S. Mill: System of Logic
Nietzsche: The Will To Power
James: Pragmatism: A New Name for Some Old Ways of Thinking
Santayana: The Life of Reason; Scepticism and Animal Faith; Realms of Being.
Russell: The Problems of Philosophy.
A.J. Ayer: Theory of Knowledge.
Chomsky: Language and Problems of Knowledge.