Nepene
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?
Brandon Sanderson
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.)
Nepene
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.
Brandon Sanderson
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.)