1. Plato, Books VI–VII; ;
2. Aristotle, Book IV;
3. Augustine, Book X; Soliloquies
4. Aquinas, I, Question 16;
5. Descartes, , IV
6. Hume, , Section IV
7. Kant, (on truth and the categories)
8. Hegel, , Preface
9. William James, , Lecture VI; The Meaning of Truth