Hume's Empiricism: Impressions, Ideas, and Knowledge

Simple and Complex Ideas: Laws of Association

1. Simple Ideas

Simple ideas are indivisible sets of impressions, such as color, smell, or taste. They do not support distinction or separation.

2. Complex Ideas

Complex ideas are formed by the combination, aggregation, or grouping of simple ideas. This is not done in a fortuitous or arbitrary way, but by virtue of the association of ideas, a trend governing how simple ideas combine.

3. The Association of Ideas

For complex ideas to form in the mind, simple ideas must associate through psychic rules:

• Similarity and Dissimilarity
• Spatiotemporal Contiguity
• Cause and Effect

By classifying the elements of knowledge into impressions and ideas, Hume laid the foundations of radical empiricism. This approach introduces a sharp criterion for determining the truth of our ideas: If we want to know if an idea is true, we must check if it originates from an impression. If we can identify the corresponding impression, we are facing a real idea; otherwise, it is a fiction. The limits of our knowledge are defined by our impressions.

Types of Knowledge and Classification

1. Relations of Ideas

These relations are formulated in necessary, tautological propositions. Their truth can be known a priori through the mere operation of the understanding. This field belongs to formal deductive sciences (arithmetic, algebra, geometry) and is governed by the principle of non-contradiction.

2. Matters of Fact

The truth of these propositions is known only a posteriori and relies solely on impressions. They represent the world of facts and belong to empirical sciences, such as natural science and moral philosophy. These do not offer absolute certainty, only probability. Physical or natural sciences deal with matters of fact and have value only insofar as they are limited to past experiences. Nothing guarantees that the future will be identical to the past; therefore, the opposite of any matter of fact is always possible.