There are people like the late Edward Nelson who represent radical formalism: https://web.math.princeton.edu/~nelson/papers/rome.pdf https://web.math.princeton.

There are people like the late Edward Nelson who represent radical formalism: https://web.math.princeton.edu/~nelson/papers/rome.pdf https://web.math.princeton.edu/~nelson/papers/rome.pdf and question the consistency of the commonly used axiomatic systems like peano arithmetic: https://www.lesswrong.com/posts/gsvQSpeDHKXxjXwuM/edward-nelson-claims-proof-of-inconsistency-in-peano https://www.lesswrong.com/posts/gsvQSpeDHKXxjXwuM/edward-nel... (Although his inconsistency proof of PA turned out to be flawed.) One should also mention Wittgensteins remarks: https://plato.stanford.edu/entries/wittgenstein-mathematics/ https://plato.stanford.edu/entries/wittgenstein-mathematics/ And in general thoughts going into the direction of ultrafinitism are quite provocative. See for example D. Zeilbergs opinions: https://sites.math.rutgers.edu/~zeilberg/OPINIONS.html https://sites.math.rutgers.edu/~zeilberg/OPINIONS.html