Hume's Empiricism: Experience, Causation, and the Limits of Knowledge

Introduction: Hume's Conservative Empiricism

In morals, politics, religion, and science, David Hume was a conservative empiricist who emphatically rejected all theories he considered metaphysical or not grounded in actual experience and sense perception. He did not regard religious and metaphysical theories as scientific, but rather as idle speculation, superstition, and prejudice. No ultimate original principles existed outside of the mind and its perceptions, and this certainly included the concept of cause and effect, which he insisted was derived from the senses and later processed through the mind in the form of simple and complex ideas. Nothing could be known about human nature — or any other subject — outside of an exact, empirical science, while innate and a priori ideas did not exist.

Even his theories of mathematics, logic, and the color spectrum were all based on empiricism and the ability of the mind to reflect, compile, and make connections based on repeated sense experiences. In short, he had no use for the complex system-building of the Continental European philosophers, although his rigid empiricism risked carrying him to the opposite extreme and reaching peculiar conclusions — such as doubts about whether physical or mathematical laws operated independently of the observer. Hume never intended to be a nihilist or subjectivist; he agreed that a real physical universe existed to be perceived, even though he denied that human beings could have meaningful knowledge about its ultimate causes. His theory did not lead to an outright denial that nothing could be known about the world, but it did make him skeptical of any universal theories or laws concerning gravitation, motion, energy, and other forces. Hume preferred to keep his theorizing closer to common, everyday experience, and to causes and effects that could be easily verified by any observer on this planet.

Sense Impressions, Ideas, and the Copy Principle

As an empiricist, Hume insisted that human beings have no innate ideas — only information derived from sense impressions. This is why metaphysics appears incomprehensible within his framework. Simple ideas are processed through mental faculties like the imagination to form complex ones, but they exist only because of "the materials afforded us by the senses and experience" (Hume, p. 11). As an illustration of this Copy Principle, Hume offers the example of a person who has seen every shade of blue except one. When shown a color chart with a blank space where that shade would appear, the person's imagination would be able to construct an idea of what that color looked like, even without having seen it directly.

All complex ideas can ultimately be analyzed and broken down into the simple ideas that are their original components; if they cannot be, they are meaningless. All ideas are connected by association — a principle Hume considered his most important contribution to philosophy. Three of the mental functions operating under this principle are resemblance, contiguity, and cause and effect. Causation was the most powerful mental function of all and the only one that extends "beyond the evidence of our memory and senses" (Hume, p. 22). For Hume, association was as vital to philosophy and psychology as Newton's laws of gravity were to physics, and it made a true science of human nature possible.