David Hume's Empirical Philosophy: Substance and Causality

Hume's Critique of the Idea of Substance

We must ask what impression derives from this idea? We cannot assign any impression to this idea. It has no reality, as the limits of our knowledge are the impressions themselves. Hume is therefore eliminating innate ideas and rejecting abstract ideas.

Impressions are always those that precede and supply the whole idea. Imagination makes its first appearance in a previous appearance. Therefore, the idea of substance can only come from our imagination, not derived from any sensitive impression.

Hume argues that the idea of substance is merely a collection of simple qualities to which we apply a particular name to remember them. This does not mean that substance is a surviving entity or a metaphysical concept. We only perceive the qualities, but this gives us no right to assert the existence of a substance underlying these qualities.

The substance is a fiction motivated by the contiguity of space and time for a constant conjunction. Bear in mind that the mind needs to form these abstractions.

Hume's Analysis of the Idea of Causality

Hume uses empirical observation to argue that traditional theories of causality are incorrect. He proposes to test causality through empirical analysis and reaches the following conclusions:

1. Causality as Habit and Custom

   Causality is a relationship that the mind establishes based on the psychological mechanisms of habit and custom. This habit is a disposition to persistent mental experience, and is the basis of our beliefs about the future. Due to repeated habit, if we think something has happened in the past, we expect it to be repeated in the future.

2. Causal Relations are Not A Priori

   Causal relations cannot be known a priori; without experience, we can never discover cause and effect. For example, analyzing the notion of 'fire' does not inherently include the notion of 'pain'. Causal relations are not relations between ideas; our knowledge of causes is only a matter of fact, meaning the opposite is always possible.

3. The Limits of Empirical Knowledge

   Our empirical knowledge is limited to sensing a repeated sequence of temporal phenomena between A and B. This does not permit us to say that A necessarily causes B, since we lack experience of all possible cases. Therefore, we cannot affirm that causality necessarily occurs.