1. Aristotle, Books I–II;
2. Marcus Aurelius, , Books II, IV, VII, X
3. Aquinas, I, Questions 44–49; Book II
4. Montaigne, , "Apology for Raymond Sebond"
5. Hobbes, , Part I Chapters 13–14
6. Descartes, , Parts II–III
7. Locke, , Chapter 2
8. Hume, , Book I, Part III
9. Kant, (on natural law);
10. Hegel, Philosophy of Nature (Introduction)