Q (Martin): Was Plato a monist or a dualist?

I am not so sure. At the top of the pyramid of knowledge, the summum bonum or supreme Good reigns by Itself: it is the supreme archetype (arché) or nous. Plato’s is a scalar ontology, the lower steps or hypostases being subservient to the higher ones (like the 5 koshas of Vedanta and the 5 levels in Sufism). Contemplation only can afford such view. I think that would make Plato a monist – or non-dualist.

A (Tom McFarlane): Despite Plato’s Theory of Forms, which is widely viewed today as a form of dualism, there is good reason to believe that Plato was not a dualist and did not view his Theory of Forms as his final position.

In fact, none other than Plato himself demolished the Theory of Forms in his Parmenides dialogue. In the first half of that dialogue, he has the character of Parmenides point out to the young Socrates all the problems and contradictions that result from such a dualistic theory.