David Hume: Empiricism, Knowledge, and Causality Critique
Hume: Empiricism Against Rationalism
Knowledge Originates from Experience
Empiricists, like David Hume, rejected the existence of innate ideas. For them, all knowledge originates from sensory experience, or as Hume called them, impressions. For an empiricist, the origin and foundation of our knowledge is experience. In contrast, rationalists defend the existence of innate ideas, from which they believe all our knowledge arises. Rationalists argue that reason can grasp these ideas independently of experience and that reason itself has no limits.
Critique of A Priori Metaphysics
Rationalists defended metaphysics as a science capable of knowing objects like God or the soul a priori, meaning independently of experience. Hume criticized rationalist metaphysics, noting its lack of progress compared to the success of the new natural sciences (like astronomy and physics). Therefore, Hume’s goal was to initiate a similar revolution in the field of social sciences or humanities, the ‘science of man’.
Hume recognized the need to study human understanding, considering all sciences related to human nature as part of this ‘science of man’. He insisted that this science must be based on experience and observation. Consequently, Hume rejected any assumption not grounded in experience.
Impressions and Ideas: Mind’s Perceptions
According to Hume, the human mind is composed of perceptions. He defined perceptions as everything the mind is conscious of and distinguished between two types:
- Impressions: More forceful and vivid perceptions (sensations, emotions).
- Ideas: Weaker copies of impressions used in thinking, remembering, and imagining.
Tracing Ideas to Impressions
Hume argued that impressions always precede ideas. Since impressions derive from sensory experience, he concluded that all ideas originate from experience. Therefore, there are no innate ideas. Hume established his first principle of human nature as a criterion for truth: for an idea to be considered valid, we must be able to trace it back to a corresponding impression. If we can find this originating impression, the idea is meaningful.
Experience Sets Knowledge Limits
However, this principle also implies that our knowledge is limited by experience. We cannot know anything for which we have no corresponding impression derived from experience.
Types of Knowledge: Ideas vs. Facts
Hume established a classification of different types of knowledge, distinguishing between:
- Relations of Ideas: These concern abstract reasoning, like geometry, algebra, and logic. They can be known a priori (independent of experience) and their denial leads to a contradiction. They state nothing about the world’s existence.
- Matters of Fact: These deal with existence, objects, and causality in the world. They are known a posteriori (through experience), and their denial is conceivable without contradiction. Matters of fact become problematic when predicting future events, as we tend to assume the future will resemble the past, even though we have no direct impressions of future events.
Hume’s Analysis of Cause and Effect
To analyze our reasoning about future events (matters of fact), Hume examined the concept of cause and effect (causality).
Observed Conditions of Causation
Hume applied his principle of the priority of impressions over ideas to the causal relationship. He stated that when we observe any instance of perceived causation, we only witness three circumstances:
- Contiguity: The cause and effect occur close to each other in space and time.
- Temporal Priority: The cause precedes the effect.
- Constant Conjunction: Similar causes have consistently been followed by similar effects in past experience.
Based on these observations, particularly constant conjunction, we label one object the ’cause’ and the other the ‘effect’. We infer a necessary connection, expecting the effect to follow the cause in the future. However, observation only shows a constant conjunction, not an inherent power in the cause to produce the effect. We have no impression of this necessary connection itself.
Causality: Habit, Not Reason
Hume argued that our knowledge of causal relationships stems solely from past experience, where we have observed objects constantly conjoined. For Hume, our belief in the uniformity of nature (the assumption that the future will resemble the past, known as the principle of induction) has no rational justification; it’s based on psychological habit or custom.
He examined the nature of belief itself. When we observe a cause, we don’t just conceive of its effect; we believe it will happen. For Hume, this belief is not a product of reason or will but a feeling or sentiment arising from habit – the custom of observing the constant conjunction.
Critique of Substance: World and Self
Besides criticizing the idea of necessary connection in causality, Hume also challenged other rationalist concepts, such as the existence of an external reality independent of our perceptions, and the notion of substance.
The Self as a Bundle of Perceptions
His critique stems from the premise that the mind only directly knows its own perceptions (impressions and ideas). Hume criticized the rationalist ideas of thinking substance (mind or soul) and material substance. He found the notion that the mind’s essence is a distinct substance (whether material or immaterial) to be untenable.
Hume argued that we only have impressions of our perceptions themselves, not of any underlying substance that ‘has’ these perceptions. Therefore, there is no impression of a ‘mind’ or ‘self’ as a continuous, unchanging substance. The mind, or self, for Hume, is nothing but a bundle or collection of different perceptions, succeeding each other with rapidity, in perpetual flux and movement.