Only a true nerd would post Nerd Self-Help on Christmas Eve. And look how many comments there were that evening!
One of those comments is such a beauty that I have to re-post its core argument:
It’s not very helpful to assign a predicate E(x) to mean “x exists”, since you are forced to conclude ∀x E(x).
After all ~∀x E(x) is equivalent to ∃x ~E(x), a contradiction.
Hours of philosophical dispute resolved with a two-liner!
Also, Scott mentions Kant’s refutation of Anselm’s ontological proof of the existence of God, which gives me an opportunity to link to Goedel's ontological proof, which fascinated me for quite a while when I first learned about it many years ago. (Nowadays it is on Wikipedia and you can easily read all the pros and cons arguments.)