What is a Number? Is it an idea or a thing? This question has been debated since Greek times, and it still remains unanswered in philosophy and science. This post examines the nature of the problem, and what its likely resolution will look like. It illustrates how the problem of numbers leads to the problem of choice, which then results in the problem of morality, which then results in questions of happiness. The resolution of these problems requires the idea of universality—namely universal ideas, universal moral principles and universal ideas about happiness.