Far from seeing Neo-Platonism as a far-fetched corruption of Plato’s thought, these thinkers emphasize the continuity between Plato and his traditional interpreters (e.g. Plotinus).

The term “unwritten doctrine” or “unwritten dogma” comes from Aristotle’s Physics

“It is true, indeed, that the account he gives there of the participant is different from what he [Plato] says in his so-called unwritten teaching (agrapha dogmata).” – Aristotle, Physics 209b

This secret teaching conforms to something said by Plato in his Seventh Letter:

“Every serious man in dealing with really serious subjects carefully avoids writing” (344c).

What are the so-called “unwritten doctrines”? Aristotle explains it as amounting to the teaching of the “One and the Dyad.” To this is often added the “third hypostasis” of Plotinus, which is “nous” or “intellect.”

Those that favor this interpretation of Plato often see Platonism as reconcilable to Christianity.

Pertinent dialogues to this debate are: Republic, Timaeus, Parmenides, Philebus, Phaedrus, Phaedo and Epistle 7.