Descartes and Hume: Philosophy of Mind and Knowledge
Descartes’ Philosophy of Mind
According to Descartes’ anthropology, the bodies of animals are not machines. What differentiates man from animals is that man also possesses an ego or consciousness. Descartes provides a somewhat simplistic explanation of the interaction between soul and body, suggesting a connection through the pineal gland. (Rationalist philosophers like Malebranche, with his occasionalism, Spinoza, with his psycho-physical parallelism, and Leibniz, with his pre-established harmony, attempted to solve this difficult problem that Descartes left pending).
Descartes believed that from understanding the interaction of imagination, ways of feeling emerge (when the understanding is passive), imagining (when the mind is active and determines the imagination), and designing (when understanding acts alone). The will, ruling on knowledge that is not clear and distinct (which is most), leads to error. Cartesian dualism, the separation of soul and body, allows Descartes to defend both absolute determinism in the physical world and freedom of the soul, without contradiction.
Hume’s Empiricism and Theory of Knowledge
Although Hume wrote on ethics, politics, religion, and history, his prominent place in the history of philosophy is primarily due to his theory of knowledge. Like all empiricists, Hume rejected innate ideas: all the contents of our mind come from experience. He called these contents “perceptions.”
There are two kinds of perception:
- Impressions: Vivid and immediate perceptions provided by our external senses (feelings) and internal senses (thoughts).
- Ideas: Derived from impressions, and are less forceful and vivid.
The mind associates ideas according to three principles:
- Similarity
- Contiguity in space or time
- Cause and effect
Objects of Reason: Relations of Ideas and Matters of Fact
Hume distinguished between two objects of human reason and inquiry:
- Relations of Ideas: These cannot be denied without contradiction (e.g., mathematical propositions).
- Matters of Fact: These rely on experience, and their denial is not contradictory (e.g., physical propositions).
This distinction, known as “Hume’s Fork,” is used to separate the true object of knowledge from the illusory.
Hume’s Critique of Causality
Hume used this distinction to examine the idea of causality. According to Hume, essential elements of the definition of “cause” are priority in time and the necessary connection of two things or events (A and B). However, this idea of causation and necessary connection is not deducible from a relationship between the ideas of A and B, nor is it empirically observed in A and B.
Hume argued that the idea of cause has no basis other than a psychological relationship: a belief based on custom. Causal inference is acceptable only between impressions: we can move from one impression to another, but not from an impression to something that has never been an impression. This is contrary to Locke, who inferred the existence of stratified reality as the cause of our impressions.
Similarly, Hume argued that the principle of causation cannot be used to substantiate the claim that God exists (as Locke and Berkeley had done). Of the three Cartesian substances (God, world, and self), only the self remained to be addressed.
The Self and Identity
Hume stated, “If any impression gave rise to the idea of self, that impression would have to remain invariably the same throughout our entire lives, since the self is supposed to exist in this way. However, there is no constant and invariable impression.” To explain the awareness of one’s own identity, Hume relied on memory, stating that the error lies in confusing succession with identity.