Abstract

This essay first takes into consideration the Kantian distinction between “ostensiveµ and “apagogicµ proofs. Then it relies on a page of Kant’s Prolegomena and on the 9th Chapter of Aristotle’s De Interpretatione in order to conclude that the apagogic inferences – which are based on the Principle of the Excluded Middle – could be produced only if an impossible condition was fulfilled. Likewise, the essay also shows – by referring to Kant’s pre-critical work Nova Dilucidatio, written in 1755 – that the ostensive proofs inevitably get caught in a vicious circle. The following overall conclusion is finally drawn: the whole rationalist tradition, as it is based on the idea that the truth must be demonstrable in order to be such, should be put into question: as a result, rational procedures such as proving, demonstrating and arguing show themselves to belong to the terrain of the opinion rather than to the dimension of the truth.