Stars and Angels

I'm listening to a Portable Professor lecture series entitled "What Would Socrates Do? The History of Moral Thought and Ethics" by Peter Kreeft. I liked this quote, though it has nothing to do with ethics. It reminds me of a discussion at a men's meeting a couple of years ago.

You’re certain that a square can’t be a circle because you understand the essence of a square and the essence of a circle. But you’re probably not absolutely certain that a quasar can’t be an angel because you don’t fully understand the essence of the quasar or an angel.