Key Ideas
1. Knowledge requires secure foundations
Beliefs inherited through habit must be tested before they can support a stable system.
2. Sensory experience is fallible
Occasional deception prevents the senses from supplying absolute certainty by themselves.
3. Dreams challenge experiential certainty
The immediate appearance of waking does not always contain a decisive guarantee that one is awake.
4. The evil genius intensifies doubt
Systematic deception is imagined to prevent familiar convictions from returning without justification.
5. The cogito is self-verifying
Thinking confirms the thinker’s existence whenever the judgement “I am, I exist” occurs.
6. The self is first known through thought
Doubting, understanding, willing, imagining and sensing are indubitable as conscious activities.
7. Judgement contributes to perception
The wax is recognised across sensory change through an intellectual grasp of its possible properties.
8. Ideas differ in representational content
Descartes ranks what ideas present and asks whether their causes possess adequate reality.
9. The idea of infinity supports a causal proof
A finite mind is said to require an actually infinite source for its idea of perfect being.
10. God is not a deceiver
Divine perfection becomes the basis for trusting cognitive faculties when they are used correctly.
11. Understanding is finite
The intellect clearly presents only a limited range of matters at any moment.
12. Will can exceed evidence
Error occurs when affirmation or denial reaches beyond clear and distinct understanding.
13. Suspension of judgement protects truth
Withholding assent is the proper response when reasons remain incomplete.
14. Mathematical essences appear necessary
Relations of extension, shape and number are grasped as more than arbitrary inventions.
15. The ontological argument links perfection and existence
Necessary existence is claimed to belong inseparably to the essence of a supremely perfect being.
16. Material things exist
Involuntary sensation and divine non-deception restore qualified belief in an external world.
17. Mind and body have different essential attributes
Mind is thinking and unextended; body is extended and divisible.
18. Real distinction does not eliminate union
Hunger, pain and thirst reveal that embodied experience is intimate rather than merely observational.
19. Sensation serves preservation
Bodily signals guide practical survival without providing infallible scientific descriptions.
20. Waking experience has coherent continuity
Memory and causal connection help distinguish organised waking life from isolated dream episodes.