1. Plato, , 202d–203a (Diotima on intermediate spirits); ; Book X
2. Aristotle, Book XII, Chapter 8 (separate substances and the movers of the spheres)
3. Plotinus, , especially Third Ennead, Tractate V; Fifth Ennead, Tractate VIII
4. Augustine, Book XII; Books IX–XII
5. Aquinas, I, Questions 50–64 (the Treatise on the Angels); Questions 106–114
6. Dante, , XXVIII–XXIX
7. Hobbes, , Part I, Chapter 34; Part III, Chapter 34
8. Milton, , Books I–II, V–VI
9. Locke, , Book II, Chapter XXIII; Book IV, Chapter XVI
10. Leibniz, ;
11. Kant, , Transcendental Dialectic;
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