This is the same response I gave to throwawaymath:

The original post is called "What even is a number?". The comment I replied to tried to answer that question with "some formalism".

What I'm saying is: questioning foundations leads you to new foundations. New foundations that you can then question all over again. It's turtles all the way down.

If you're actually looking to use math, this is a futile exercise. It works, so just use it. Essentially, I am re-iterating von Neumann's statement:

> In mathematics you don't understand things. You just get used to them.