I cain’t use fancy words like “epistemic” and “peano” so good, but I think I can attempt to translate what Liberal is saying.
First of all, there’s this thing called mathematics. It’s a purely intellectual exercise. It is a system of statements and ideas, inside an axiomatic framework. One of the neat things about it is that in mathematics, unlike just about anything else, it IS possible to prove things with 100% accuracy. For instance: “there are an infinite number of prime positive integers”. That statement is just plain TRUE, not ifs, ands or buts.
Now, mathematics, by itself, is just a mental game. It’s cool, it’s neat, it’s deep, but what’s REALLY useful about it is that it with incredible frequency is useful for describing the universe. So it is possible, in a fashion that is extremely easy for us to do (counting), to associate a positive integer (which is just an imaginary construct) with a “set” (using the term loosely) of real world items, like apples.
So I can observe that if I have a set of apples whose count is 3, and add them to a set of apples whose count is 7, I’ll get a set of apples whose count is 10. And, fortunately, 3+7=10.
What I can NOT do is PROVE with the same 100% level of no-ifs-ands-or-buts certainty that there will be 10 apples. I can perform the experiment over and over. I can propose a hypothesis, which would be something like “simple mathematical arithmetical induction corresponds precisely to the adding-sets-of-apples-together operation”. I can test that hypothesis. But all I can do is collect more and more and more evidence that suggests that the hypothesis is true. There’s never any final last step where, once I’ve done it, the proof is complete, and we now know that, forevermore, apples will always be addable.
And in general, in fact, there are times when math DOESN’T describe the universe. If I have a drop of water, and I add a drop of water to it, what do I get? One drop of water? Or two drops of water? What if I was trying to count something that was kind of like an apple, but kind of like a drop of water? What if I added 2 bunnies to 2 bunnies, came back several months later, and got 20 bunnies?
Many things in the real world correspond in various ways to imaginary things in math. Which is a damn good thing, because science would be FUBARed without it. But proving something in math is ABSOLUTE PROOF. Proving something in the real world is just VERY LIKELY, WITH LOTS OF EVIDENCE.