 From these general considerations about the nature of mathematics, based on the condition of the human mind (Moore 2001), intuitionists infer to a revisionist stance in logic and mathematics. They find non-constructive existence proofs unacceptable. Non-constructive existence proofs are proofs that purport to demonstrate the existence of a mathematical entity having a certain property without even implicitly containing a method for generating an example of such an entity. Intuitionism rejects non-constructive existence proofs as ‘theological’ and ‘metaphysical’. The characteristic feature of non-constructive existence proofs is that they make essential use of the principle of excluded third