David Hume’s Philosophy: Knowledge, Causality, and Substance
David Hume
Theory of Knowledge
Hume defined perception as everything that is present in our minds, and he identified two types:
- Impressions: Knowledge gained through the senses.
- Ideas: Representations or images of perceptions in thought, which are derived from impressions and are less intense.
Impressions serve as the criterion of truth for ideas because an idea is true if we can identify it as coming from an impression. Hume also distinguished two ways of knowing:
- Knowledge of relationships among ideas does not concern facts but rather the relationship between ideas, and its truth does not depend on any facts. For example, “A square has four sides.” This is expressed in analytic judgments.
- Knowledge of facts concerns the facts and is based on experience.
Critique of the Idea of Cause
Our knowledge is limited to perceptions: current impressions and memories (ideas). However, there can be no knowledge of future events because we have no impression of what will happen.
Often, we assume that certain events will take place in the future, and this certainty is based on a causal inference. For example, if it rains on something, that something gets wet.
The idea of cause is the basis of these inferences about facts for which we have no current impression (e.g., rain). This resolution (e.g., wet) is conceived as a necessary connection between cause and effect. However, we do not have an impression of this connection if the effect is in the future tense. We only know that between cause and effect, a constant succession takes place (e.g., whenever it rains on something, then that something gets wet). Since our knowledge is limited to impressions and ideas, and we have no impression of a necessary connection, we do not know that this will happen; we only believe it will.
Thus, knowledge of future events is a belief due to habit, and the cause-effect relationship can only be applied if both are impressions because the cause is not a sensible quality of things.
Similarly, Hume denied the existence of innate ideas because they are formed from impressions and do not provide a foundation for science. We cannot know of the existence of any substance.
Critique of the Three Types of Substance
- The World: The belief that there are corporeal realities different from our impressions, based on the fact that we have impressions of them, is a misapplication of cause and effect.
- God: We cannot affirm the existence of God as the cause of our existence since we cannot have any impression of God. This is another misapplication of the cause-effect relationship.
- The Self: We cannot justify the existence of the self as an impression of oneself because we only have intuition of our impressions and ideas, not of ourselves. To explain the sense of self-identity, Hume uses memory, which allows us to recognize the relationship between impressions.
Comparison with Hobbes on the Philosophy of History
For both Hume and Hobbes, sociability arises from a pact, a social contract. For them, man’s natural state is a prosocial state.
Differences:
- Hobbes used a hypothesis that the state of nature must be an ongoing war since “man is a wolf to man.” He assumed that there comes a time when this situation forces man to establish a social pact to preserve life and establish private property, which is an artificial agreement.
- For Kant, the “state of nature” was a state of savage and lawless freedom in which man lives under the threat of violence because everyone does as he pleases. He considered that the social pact is the first moral obligation that we set for ourselves: to leave the state of nature and seek peace, justice, and freedom.