Hume vs. Descartes: Empiricism & Rationalism Compared

Hume vs. Descartes: Core Philosophical Differences

David Hume, a prominent empiricist, argued that knowledge stems fundamentally from experience. He famously used the example of pool balls to illustrate that we cannot logically deduce a cause-and-effect relationship between two successive events merely through reason; we only observe constant conjunction. For Hume, our belief in causality is an unjustified product of the mind, guided by custom or habit, arising from repeated observations.

Both Hume and René Descartes sought to justify their doubts about existing knowledge and outlined methods for finding absolute truth. However, their approaches differed significantly. Hume started from sense perception and used induction (forming general laws from specific observations or feelings), while Descartes employed a logical deductive process (inferring specific facts from general laws or principles).

Empiricism and Rationalism Defined

Hume was an empiricist. Empiricism, like its counterpart rationalism, focuses on the nature and acquisition of knowledge. Empiricism asserts that knowledge comes primarily from sensory experience. Key representatives include John Locke (Baroque period), George Berkeley, and David Hume (English Enlightenment). Rationalism, conversely, emphasizes reason as the chief source and test of knowledge. Its main proponents were René Descartes, Gottfried Wilhelm Leibniz, Baruch Spinoza, and Nicolas Malebranche.

Hume on Perception: Impressions and Ideas

Hume distinguished between two types of mental perceptions:

• Impressions: These are the immediate, vivid data of sensory experience (e.g., hearing a sound, feeling warmth).
• Ideas: These are fainter copies or recollections of impressions left in the mind after the sensory experience has passed (e.g., remembering the sound, thinking about warmth).

He further divided perceptions into simple (indivisible) and complex (divisible into simpler parts).

Critique of Metaphysics and Substance

Based on his principles, Hume critiqued traditional metaphysics. He denied the meaningfulness of the idea of substance (an underlying reality holding properties together), arguing that it does not correspond to any specific sensory impression. We only perceive a collection of qualities, not an underlying substance itself.

Contrasting Methodologies: Induction vs. Deduction

While Descartes looked to mathematics, specifically Euclidean geometry, as the model for knowledge and method, Hume admired Newtonian physics. Descartes utilized the hypothetical-deductive method, moving from universal principles to particular conclusions. Hume, conversely, employed the inductive method, generalizing from particular observations to broader, though potentially less certain, universal claims. Consequently, Hume believed that most knowledge derived from experience is probable, not absolutely certain.

The Debate on Innate Ideas

Descartes believed in the existence of innate ideas – truths inherent in the human mind from birth, which are undeniable and secure. Hume strongly rejected this, famously comparing the mind at birth to a tabula rasa (a blank slate) upon which experience writes.

Criteria for Truth: Evidence vs. Correspondence

Their criteria for truth also diverged. For Descartes, the criterion was evidence: something is true if reason perceives it clearly and distinctly, making it self-evident. For Hume, the primary criterion was correspondence: an idea is meaningful or true only if it corresponds to, or can be traced back to, a sensory impression.

Differing Concepts of 'Idea'

Although both philosophers considered knowledge to be fundamentally about ideas, their understanding of 'idea' differed. Descartes viewed ideas as representations, potentially like lenses, through which we perceive reality. For Hume, an idea was simply a faint copy of a prior sensory impression.

Hume's rigorous empiricism ultimately led him towards skepticism (doubting the possibility of certain knowledge, especially regarding the external world, causality, and the self) and phenomenalism (the view that we can only know phenomena or appearances, not any underlying reality).

Sources of Philosophical Doubt

Descartes: Doubting the Senses

Descartes doubted the reliability of sensations because they had deceived him on numerous occasions, most notably in dreams, where experiences feel real but aren't.

Hume: Questioning Logical Prediction

Hume questioned the power of pure logic or reason to predict future events or establish cause and effect. He argued that such matters of fact can only be known through observation and experience, not a priori reasoning.