epistemology (ĬpĬs´təmŏl´əjē) [Gr.,=knowledge or science], the branch of philosophy that is directed toward theories of the sources, nature, and limits of knowledge. Since the 17th cent. epistemology has been one of the fundamental themes of philosophers, who were necessarily obliged to coordinate the theory of knowledge with developing scientific thought. Réné Descartes and other philosophers (e.g., Baruch Spinoza, G. W. Leibniz, and Blaise Pascal) sought to retain the belief in the existence of innate (a priori) ideas together with an acceptance of the values of data and ideas derived from experience (a posteriori). This position was basically that of rationalism. Opposed to it later was empiricism, notably as expounded by John Locke, David Hume, and John Stuart Mill, which denied the existence of innate ideas altogether. The impressive critical philosophy of Immanuel Kant had immense effects in an attempt to combine the two views. In later theories the split was reflected in idealism and materialism. The causal theory of knowledge, advanced by Alfred North Whitehead and others, stressed the role of the nervous system as intermediary between an object and the perception of it. The methods of perceiving, obtaining, and validating data derived from sense experience has been central to pragmatism, with the teachings of C. S. Peirce, William James, and John Dewey. Sir Karl Popper developed the view that scientific knowledge rests on hypotheses that, while they cannot be positively verified, can be proven false and have withstood repeated attempts to show that they are. Philosophers in the 20th cent. have criticized and revised the traditional view that knowledge is justified true belief. A springboard for their research has been the thesis that all knowledge is theory-laden.
See A. D. Woozley, Theory of Knowledge (1949, repr. 1966); J. Dancy, Introduction to Contemporary Epistemology (1985); A. J. Ayer, The Problem of Knowledge (1956, repr. 1988).