1. Plato, , Books V-VII; Apology
2. Aristotle, , Books I-II
3. Epictetus, , Books I-II
4. Augustine, , Books III, VII; , Books VIII, XIX
5. Aquinas, , I, Q. 1; , Book I
6. Bacon, , Book I
7. Descartes, ; , Meditation I
8. Hume, , Sections I, XII
9. Kant, , Prefaces, Introduction