Introduction; 1. Why Cannot the ti esti Question Be Answered by Example and Exemplar? Hippias Major; 2. Why Cannot Essences, or Forms, be Perceived by the Senses? Hippias Major. Phaedo. Republic; 3. Why are Essences, or Forms, Unitary, Uniform and Non-Composite? Why are they Changeless? Eternal? Are they Logically Independent of Each Other? Phaedo and Republic; 4. The Relation between Knowledge and Enquiry in the Phaedo; 5. Why are Essences, or Forms, Distinct from Sense-Perceptible Things? Phaedo 74 and Republic V. 478–479; 6. Why are Essences, or Forms, the Basis of all Causation and Explanation? Phaedo 95–105; 7. What is the Role of Essences, or Forms, in Judgements about Sense-Perceptible and Physical Things? Republic VII. 523–525; 8. Why does Thinking of Things Require Essences, or Forms? Parmenides; 9. Why are Essences, or Forms, Separate from Physical Things? Also Timaeus and Philebus; 10. What Yokes Together Mind and World? Phaedo 99–100 and Republic VI. 505–509; Conclusion: Forms Simply are Essences, not Things that have Essences.