David Hume's Philosophy: Perceptions, Causality, and Ethics

Hume's General Lines of Thought

Knowledge for Hume is rooted in perceptions, which he divides into impressions and ideas.

Impressions and Ideas

Impressions are perceptions that are more alive and strong, yet they are perishable. There are two types of impressions:

• Sensation: Arising in the mind from unknown causes.
• Reflection: Derived largely from our ideas.

The difference between impressions and ideas is the degree of force and vivacity; it is the difference between feeling (seeing, touching, etc.) and thinking (remembering, imagining).

Simple and Complex Ideas

Ideas are copied from our impressions and are divided into:

• Simple ideas: These correspond directly to an impression.
• Complex ideas: These are formed from simple ideas, such as the concept of a siren.

Laws of Association and Causality

To join simple ideas in our mind, there are specific laws of association: resemblance, contiguity, and cause and effect. Hume criticizes the relation of cause and effect, demonstrating that this connection lies within ourselves and is acquired by custom.

Types of Propositions

He distinguishes between two types of propositions:

• Relations of ideas: Found in formal sciences like mathematics and logic. These provide certain knowledge, and their opposite is impossible.
• Matters of fact: Found in the rest of science; these are empirically verifiable, and their opposite is always possible.

Causation as Experience and Belief

Hume distinguishes between a philosophical account of causation—where the cause-effect relationship is based on intuitive experience—and causality as a natural relationship. If one can conceive of a change in nature, it can also occur between a cause and effect; thus, all we truly have is feeling or belief.

The Criticism of Substance

Hume employs a similar strategy in his criticism of substance, both material and spiritual. He argues that substance is merely a collection of simple ideas grouped by the imagination under a single name.

Material and Spiritual Substance

Regarding material substance, we believe in the existence of bodies independently of us without direct impressions of them. This belief is imposed on us as the imagination provides consistency and coherence to our perceptions, creating the "fiction" of continued existence.

The spiritual substance, according to Hume, is a collection of perceptions in perpetual flux and movement. He denies that we have a direct perception of "ourselves," stating that the mind is constituted only by the perceptions that flow through it.

Ethics and Moral Sentiment

In the field of ethics, Hume believes that our behavior involves both sense and reason. He argues that the cause of acting in a certain way—preferring one thing over another—is not rooted in knowledge. Therefore, reason alone does not make us act. From a rational point of view, one cannot move from an "is" to an "ought" (should be).

Thus, Hume concludes that feeling is what makes us want, and a feeling of sympathy toward the human genre serves as the foundation of moral value. This feeling is carried or lost over time, so we must educate with feeling; for example, you will never convince anyone that lying is wrong if they do not feel it.