What are the major open questions of mathematical philosophy? Of these, which are mathematically significant, if any? By "mathematically significant," I mean "would affect the way mathematicians work." For example, the question of whether mathematics is created or discovered has no impact on working mathematicians. On the other hand, studies into the foundations of Math were certainly mathematically significant, and although one could argue that that was more Math than Phil, we can give Phil some credit. But that question is now closed, as far as mathematicians are concerned.