David Hume: Critique of Substance and Metaphysics

Hume's Criterion of Truth and the Idea of Substance

Hume questioned the validity of the idea of substance, making use of the criterion of truth to determine the validity of an idea. An idea is true if it is derived from an impression; otherwise, we consider it false. However, there are only two kinds of impressions:

• Impressions of sensation
• Impressions of reflection

The Role of Impressions and Imagination

There is no impression of sense which corresponds to the idea of substance because this idea does not contain anything sensitive. The idea of substance does not correspond to any impression, and an idea that is not derived from any impression is false. The idea of substance is produced by the imagination.

The Problem of External Objects and Perception

We have a natural tendency to believe in the existence of bodies regardless of our perceptions. But if you look at the issue philosophically, says Hume, it shows that this belief is entirely unfounded. In fact, we are 'locked' in our perceptions and cannot go beyond them, as they are all that is shown to the mind.

Causality and the Limits of Reason

If we tried to apply the principle of causality to show that our impressions are caused by external objects, we would incur an illegitimate application of that principle, since we only record our impressions. The belief in the independent existence of external objects Hume ascribes to the imagination, because of the constancy and coherence of perceptions. You cannot justify such a belief supported by the senses or appeals to reason. It cannot come from the senses because they do not offer us anything different from our perceptions.

Neither could reason be the basis for such a belief; it is not possible to use the principle of causality or the idea of substance to justify the existence of external objects independent of my perceptions.

Critique of the Soul and the Self

For the metaphysical tradition, the soul's existence—as a substance, material or immaterial, subsistent, and the ultimate cause or subject of all my mental activities—had represented one of the pillars on which it had developed. Having rejected the validity of the idea of substance, we can no longer maintain the idea of the soul, of a substrate, or a subject which remains identical to itself, simple and distinct from its perceptions.

What leads us to attribute simplicity and identity to the self is a confusion in the mind between the ideas of 'identity' and 'succession', to which the action of memory must be added.

Metaphysical Proofs and the Existence of God

Given the criticisms levied against the idea of substance and the principle of causality, Hume will not recognize any validity in metaphysical proofs of God's existence, considering that it is not rationally demonstrable. If the idea of substance is a misconception, the only argument that seems to have some capacity for belief is that which starts from the world order to suggest the existence of an intelligent ordering cause. Hume added that this argument attributes to the cause only the qualities that are necessary to produce the effect.