You've mentioned several philosophical concepts used in the writing of your books, like Jung's collective unconsciousness, Plato's cave. Could you expand a bit on your use of those in your books, and whether you think it is necessary to use philosophy to make a good fantasy world?
I don't think it's necessary at all. The writer's own fascinations--whatever they are--can add to the writing experience. But yes, some philosophical ideas worked into my fiction. Plato's theory of the forms has always fascinated, and so the idea of a physical/cognitive/spiritual realm is certainly a product of this. Human perception of ideals has a lot to do with the cognitive realm, and a true ideal has a lot to do with the spiritual realm.
As for more examples, they're spread through my fiction. Spinoza is in there a lot, and Jung has a lot to do with the idea of spiritual connectivity (and how the Parshendi can all sing the same songs.)
Not completely sure where Spinoaza comes in. I guess the shards are part of the natural world and have no personality without a human wielder.
Yes on Spinoza there, and also the idea of God being in everything, and everything of one substance. Unifying laws. Those sorts of things. (Less his determinism, though.)