The Concept of Existence in Mathematics

Abstract

We assert that, from a pragmatic point of view, mathematicians treat mathematical objects as if they were real. If a theory is consistent, theorems are discovered (sometimes with analyses not necessarily different from those applied in sciences) and proofs are invented; modern technology cannot exist without accepting the law of excluded middle; a constructive proof may provide new ideas or methods but, from a mathematical point of view, a non-constructive proof is as sound as a constructive one. Accordingly, no mathematician, pure or applied, gets by without the axiom of choice; on the other hand, although different theorems and objects may appear depending on the acceptance or not of the continuum hypothesis, no important theorem applicable to the real world exists – at least until now – which depends on accepting or not this hypothesis. Mathematical objects built by applied mathematicians are often as useful as physical objects, even those objects created via computer-assisted or probabilistic methods.