Key Ideas
1. Reason requires direction
Differences in judgement arise not only from ability but from the paths along which thought proceeds.
2. Inherited learning may lack secure foundations
Education provides valuable tools without guaranteeing agreement or certainty.
3. Accept only what withstands doubt
The first rule protects judgement from haste and prejudice.
4. Divide complex problems
Analysis makes difficult questions manageable by identifying their simpler components.
5. Proceed from simple to complex
Ordered construction allows later conclusions to rest upon intelligible earlier steps.
6. Review for completeness
Enumeration checks that no relevant element or inference has been overlooked.
7. Method must become a habit
Rules succeed through repeated disciplined practice rather than mere memorisation.
8. Practical life cannot wait for perfect certainty
A provisional morality permits stable action while theoretical beliefs are reconsidered.
9. Decisiveness can be rational under uncertainty
Once a reasonable direction is chosen, firmness may be better than endless hesitation.
10. Self-mastery is more attainable than control of fortune
Directing judgement and desire reduces dependence upon external events.
11. Doubt is methodological
Its purpose is to discover secure foundations, not to make permanent scepticism an end.
12. Thinking confirms existence
The attempt to doubt reveals an undeniable thinking activity: “I think, therefore I am.”
13. The mind is known before the body
The thinking self remains certain even while the existence of material things is doubted.
14. Clear and distinct ideas provide a truth criterion
Properly attentive reason seeks perceptions free from confusion and hidden mixture.
15. God guarantees non-deceptive reason
Descartes uses divine perfection to extend confidence beyond the immediate cogito.
16. Nature can be explained mechanically
Matter, motion and organisation can account for many physical and physiological processes.
17. Language indicates flexible rational thought
Open-ended meaningful speech distinguishes reason from fixed mechanical response in Descartes’ argument.
18. Experiments discriminate among possible effects
Observation becomes essential when general principles permit several particular outcomes.
19. Science should improve human life
Knowledge of nature promises practical benefits, especially more reliable medicine.
20. Inquiry needs both criticism and independence
Publication allows correction and collaboration, while excessive controversy can obstruct sustained research.