David Hume: Empiricism, Causality, and Metaphysics
David Hume: The Completion of Empiricism
Life and Work
Hume’s most important work is A Treatise of Human Nature, along with An Enquiry Concerning Human Understanding and An Enquiry Concerning the Principles of Morals. His philosophy aimed to justify and legitimize human knowledge through empiricism and illustration. Recognizing the challenge of attaining certain knowledge, Hume focused on studying human nature. He believed empirical knowledge, not innate ideas, was the key to understanding human nature. His first step was analyzing the mental processes by which we acquire knowledge, followed by addressing Cartesian metaphysical problems (the three substances).
Impressions and Ideas
Hume argued that all perceptions originate from experience, rejecting innatism. He categorized perceptions based on:
- Accuracy: Impressions (sensations from experience) and Ideas (faint copies of impressions).
- Origin: Perceptions of sensation (from external senses) and perceptions of reflection (mental states like boredom).
- Composition: Simple (indivisible) and Complex (divisible into simpler perceptions).
Psychological and Epistemological Empiricism
Hume’s principle that every idea is a copy of an impression eliminates innate ideas. This epistemological empiricism rejects metaphysical concepts like the soul or substance, as they lack empirical origin.
Imagination and Memory
While simple ideas derive from simple impressions, complex ideas aren’t always direct copies of complex impressions. For example, the idea of a unicorn combines impressions with imagination. Imagination combines impressions to form complex ideas, sometimes fancifully, but often following laws of association:
- Similarity: Ideas are associated based on resemblance.
- Contiguity in space and time: Ideas are linked by spatial or temporal proximity.
- Cause and effect: Repeated temporal succession creates an expectation of future occurrences.
Hume believed our mental content consists of impressions and ideas, which form judgments. These judgments fall into two categories:
- Relations of ideas: True by definition, these propositions establish relationships between ideas and concepts. They are universal, necessary, and their negation implies contradiction (e.g., a triangle has three sides).
- Matters of fact: Known through experience, these propositions establish relationships between observed events. Their denial doesn’t imply contradiction (e.g., it is raining).
The Problem of Causality
Hume questioned the causal relationship, applying his empiricist principle. While we perceive impressions as originating from the material world, the idea of a material substance causing these impressions lacks a corresponding sensory impression. Hume argued that cause and effect isn’t an objective law but a mental habit of associating ideas based on observed regularities. We project past experiences onto the future, forming beliefs based on custom, not universal knowledge.
The Probability of Science
Hume’s critique of causality challenges science, as many scientific descriptions and predictions rely on causal relationships. If causality is a mental habit, science becomes a belief system based on custom, not objective knowledge.
Critique of Metaphysics
Hume’s empiricist principle rejects metaphysics as it doesn’t fit into his categories of knowledge. He criticizes the idea of substance, arguing that we have no impression of substance itself, only of its qualities. Therefore, the idea of substance is not empirically grounded.