David Hume's Epistemology: Impressions, Ideas, and Knowledge Types

Hume's Empiricism: Experience and the Origin of Ideas

David Hume believes that experience is the source of all knowledge. He asserts that initially, we only know that some of the representations that appear in consciousness are very sharp and intense, while others are faint. The first are called impressions (which may involve feeling or sensing). The latter are called ideas (which involve thinking). Assuming that impressions originate in the outside world is merely an assumption that Hume will investigate. True to the empiricist principle of admitting as true only what is the product of pure experience, Hume sets the fundamental rule of his work:

The Correspondence Principle

There can be no other source for ideas than impressions. Every idea must correspond to impressions from which it is derived.

Simple Ideas and Complex Ideas

It is clear that the mind contains ideas that do not reproduce any single impression directly. This is because not all ideas are simple. As discussed in the context of Locke, there are complex ideas resulting from the aggregation of many simple ideas in the mind that have no direct connection with any single impression—a winged horse, for instance. However, the simple ideas, the constituent parts that make up a complex idea, must necessarily come from impressions received previously. The result: a term for which we cannot find the corresponding experience means nothing; it is empty, mere fiction. (Anything that does not come from experience is meaningless.)

Hume's Two Kinds of Knowledge

Although every idea should have its origin in impressions, once we have ideas, Hume distinguishes two kinds of knowledge:

1. Relations of Ideas

   These are mathematical and logical propositions that are necessarily linked to the definition of things, regardless of whether those things exist or not. The denial of such knowledge is contradictory. Relations of Ideas are, therefore, of maximum certainty, but they do not report the existence of any object; they only state the conditions that an object must necessarily meet if it exists.

2. Matters of Fact

   These deal with what actually happens, known from experience and not by demonstration. Statements concerning Matters of Fact do not possess the necessary character that distinguishes Relations of Ideas: they are contingent—their opposite is possible. Experience tells us that something has gone one way, but it could well have gone another way.

The Radical Conclusion

Hume concludes that all our knowledge consists solely of Relations of Ideas and Matters of Fact, both arising in one way or another from experience. Hume applies this radical and uncompromising stance, resulting in a full-fledged critique of traditional theology and metaphysics.