The Critique of Pure Reason, Part 9, Chapter 3 summary

What happens

1. The speaker distinguishes a system organized by one governing idea from a collection assembled around accidental purposes.
2. He separates knowledge received from others from knowledge independently grounded in principles, and distinguishes philosophy from mathematics.
3. He presents philosophy as serving reason’s ultimate aims, with moral philosophy concerned with humanity’s destiny.
4. He divides pure philosophy into criticism and metaphysics, then distinguishes the metaphysics of nature from that of ethics.
5. He maps speculative metaphysics into ontology, rational physiology, rational cosmology, and rational theology, excluding empirical psychology except as an appendix.
6. He defends metaphysics as a necessary check on speculative error and a guide toward human happiness.

What to notice

The distinction separates repeating a doctrine from exercising reason. Genuine philosophical activity includes testing principles and retaining the freedom to reject them.

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