Why cannot the ti esti question be answered by example and exemplar? Hippias Major
Why cannot essences, or forms, be perceived by the senses? Hippias Major. Phaedo. Republic
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
The relation between knowledge and enquiry in the Phaedo
Why are essences, or forms, distinct from sense-perceptible things? Phaedo 74 and Republic V. 478-479
Why are essences, or forms, the basis of all causation and explanation? Phaedo 95-105
What is the role of essences, or forms, in judgements about sense-perceptible and physical things? Republic VII. 523-525
Why does thinking of things require essences, or forms? Parmenides
Why are essences, or forms, separate from physical things? Also Timaeus and Philebus
What yokes together mind and world? Phaedo 99-100 and Republic VI. 505-509
Conclusion: Forms simply are essences, not things that have essences.