Platonism, according to one unsympathetic commentator, "assimilates mathematical enquiry to the investigations of the astronomer: mathematical structures, like galaxies, exist, independently of us, in a realm of reality which we do not inhabit but which those of us who have the skill are capable of observing and reporting on."¹ I will call this the "π in the sky" view of mathematics, but not scornfully—though perhaps with touch of self-mockery—since I think it is true. Mathematics, I shall argue, is best accounted for by appeal to real platonic entities; not only do they provide the grounds for mathematical truth, but these abstract objects are also somehow or other responsible for our mathematical intuitions and insights.