Heraclitus & Parmenides

Heraclitus claims that sense perception alone cannot reveal the truth about things, for they are not really what they seem to be. Thought is required to reveal that what seems stable is really constantly changing--that what seems to be a thing is but a slice of a process. Heraclitus invents the distinction between appearance and reality. Perceptual objects are not the real entities constituting the natural world; they are only the ways those entities appear to us. Our perceptions are the effects of causes which we do not directly perceive and which we can know only by inference. (Does the image on the movie screen or the television monitor exist? Is it a real thing in the world? Do we exist or are we more like a movie or a television program--processes seeming to be entities only because of the abstractive character of our experience of ourselves?)

Parmenides takes note of Heraclitus' observations about sense perception but disagrees that the mind could ever reconstruct the truth out of the sensory data. There is no one way our sensations can be manipulated to yield a single, coherent story about what really exits. Therefore any single way in which they are assembled will at best be an opinion, not the truth, about what is. If the truth is to be gotten, it must consist just of that information which can be acquired by the mind alone, uncontaminated by sensory information which may be understood in a variety of ways. This additional epistemological requirement Parmenides adds to the Heraclitean analysis is, in effect, the distinction between a priori and a posteriori. A priori information is that which can be acquired by pure reasoning, "prior to" perceptual experience; a posteriori information is that which initially depends on (is "posterior to") some perceptual experience. On Parmenides' view, all genuine knowledge is a priori; any a posteriori claims are necessarily only matters of belief, not of truth. Knowledge consists of truths. A truth is a proposition to which our reasoning compels us to assent; a belief is a proposition to which we voluntarily assent, since our reasoning permits more than one opinion about the matter. Beliefs cannot constitute knowledge because they compete with other beliefs and so any one belief may be false. Therefore reality can only be apprehended by a priori reasoning; any reasoning which begins with sensory data (a posteriori reasoning) can never get beyond mere appearance.

Copyright © 1998, James Dye

Last Updated 25 January, 1998