Modern Philosophy: Descartes and Hume
The modern block contrasts rationalism and empiricism. The exam wants Descartes' doubt explained as a chain of reasons ending in an indubitable foundation, and Hume's science of human nature explained as an account of how ideas are generated and whether they are justified.
Descartes: doubt, cogito, God
The method suspends assent to anything that admits the least doubt: the senses deceive, the dream hypothesis removes the external world, the evil demon threatens even mathematics. The aim is foundational, not sceptical. The cogito - "I think, therefore I am" - is an intuition, not a syllogism: every act of thinking reveals an existing thinker. The criterion of clear and distinct perception then needs a guarantee, which Descartes supplies through the proofs of God's existence, including the ontological argument, and God's veracity. Mind and body are really distinct substances (res cogitans, res extensa), yet united in the human being.
Hume: impressions, causation, the self
All perceptions divide into impressions (lively) and ideas (faint copies); the copy principle ties every legitimate idea to some impression. The fork separates relations of ideas (a priori, certain, analytic) from matters of fact (empirical, probable). Causal inference rests on constant conjunction and custom, not on any observed necessary connection, and induction has no rational justification. The self is a bundle of perceptions; personal identity is a fiction generated by imagination. Hume also notes the gap between is and ought.
Worked example
On the billiard ball: we see one ball strike another and then motion. We never perceive a "power" transferring motion - only conjunction and succession. The idea of necessary connection arises when repeated experience produces a habit of expectation in the mind. So the reasoning is: no impression of power → no genuine idea of power → causality is a felt determination, not a perceived relation.
Traps
- Presenting the cogito as a syllogism with "everything that thinks exists" as a premise.
- Treating Cartesian doubt as real scepticism rather than method.
- Saying Hume denies that causes operate - he denies that we perceive or rationally justify necessity.
- Confusing impression with opinion, or the copy principle with the fork.