"Well, it depends what you mean by true or false. Mathematics doesn't make any substantive claims, we just make conditionals. You start with some axioms, and then deduce from there. So all mathematical knowledge is conditional: if the axioms are true, then this deduction is true."
Why isn't this quite right?
First, this avoids answering basic questions about really basic math. Is 2+2=4 true or false? Can we only talk about it being true in Peano's world, or true in ZFC's world, but can't talk about it being absolutely true or false? What explains our choice to study the worlds where 2+2=4 is true instead of false? Is it just by whim? Can we then imagine living in a world where 2+2=5? Or maybe we pick the system because it matches up with our world. But doesn't that mean that we believe that 2+2=4 is really true? In that case we are committed to the existence of actual numbers. And if we want to maintain that there are no such things as number, we then have to explain why we study 2+2=4, and we have to explain why that statement seems to incredibly true about our world.
Second, it evades answering questions about the axioms. How do you choose which axioms to study? Why are we picking some axioms instead of others? If we're picking axioms that properly describe the geometry of earth, does that mean that we're studying something factual when we study that geometry? When it comes to set theory, and the foundations of things like arithmetic, we might be less willing to be wishy washy about which axioms are true. This argument is somewhat dependent on the one right above.
Third, Hilbert tried to be a formalist, but most folks think that he failed because there are tremendous tensions in trying to believe that we just work with a bunch of formal systems that are consistent when these systems can't prove their own consistency.
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