The paper analyses a basic gap, highlighted by most of the literature concerning the teaching of proofs, namely, the distance between students' argumentative and proving processes. The analysis is developed from both epistemological and cognitive standpoints: it critiques the Toulmin model of reasoning and introduces a new model, the Logic of Inquiry of Hintikka, more suitable for bridging this gap. An example of didactical activity within Dynamic Geometry Environments is sketched in order to present a concrete illustration of this approach and to show the pedagogical effectiveness of the model. Keywords Proof Á Logic of inquiry Á Argumentation Á Dynamic geometry environments 10.1 Introduction In their wonderful book Anschauliche Geometrie, Hilbert and Cohn-Vossen (1932) wrote 1 : In mathematics, as in all scientific research, we find two tendencies: the tendency to abstraction-it seeks to work out (herauszuarbeiten) the logical points of view from the manifold material and bring this into systematic connection-and the other tendency, that