1. Plato, , Book X; , 27c-42e
2. Aristotle, , Book XII
3. Augustine, , Books VIII, XI; , Book VII
4. Aquinas, , I, Q. 1; , Books I-II
5. Montaigne, , "Apology for Raymond Sebond"
6. Bacon, , Book II
7. Descartes, , Meditations III, V
8. Hume, ; , Section X-XI
9. Kant, , Transcendental Dialectic, "The Ideal of Pure Reason"