If humans didn’t exist would the idea of a chair still exist on some plane, or is it only in our minds?
I think most today would say it’s in our heads—-and so is mathematics—-yet it’s still thought-provoking.
Notice that even the universe follows that structure.
I didn't mean "a chair" i meant the [universal idea](https://en.wikipedia.org/wiki/Universal_(metaphysics)) of chair.
Plato conceived of Truth as being the light through which things could be conceived. At the highest level was ideas (eg the idea of "Chair", not any particular chair), below that was mathematical objects, followed by physical objects and then shadows.
So Plato would say that math is closer to truth than a chair, but not than the idea of Chair.