"There are lots of cases where we know more about how the world works than we do about how we know how it works. That's no paradox. Understanding the structure of galaxies is one thing, understanding how we understand the structure of galaxies is quite another. There isn't the slightest reason why the first should wait on the second and, in point of historical fact, it didn't. This bears a lot of emphasis; it turns up in philosophy practically everywhere you look."