&gt;It’s essentially the only mental construct that has evidence to support its validity.

Not sure what this means. All our words are "constructs" (though arguably not mental, but public) but we depend on them constantly in our interactions with the world. No sailor is questioning the "validity" of 'starboard', for example. The value of "constructs" comes from the use we make of them, and their role in gluing society together. I would say the value of pure mathematics, besides being an interesting endeavour in and of itself, is ultimately *applied* mathematics. In this regard I guess it's true that mathematics depends to some extent on the world: applied mathematics would be useless if objects, for example, didn't hang together over time or if they constantly multiplied randomly. But this doesn't support mathematics' *validity*, it supports its *usefulness*.