Dag Prawitz on proofs, operations and grounding Antonio Piccolomini d’Aragona antonio.piccolomini-daragona@etu.univ-amu.fr Aix-Marseille Univ, CNRS, CEPERC, Aix-en-Provence, France Universit` a degli Studi “La Sapienza” di Roma Abstract Dag Prawitz’s theory of grounds proposes a fresh approach to valid inferences. Its main aim is to clarify nature and reasons of their epis- temic power. The notion of ground is taken to denote what one is in possession of when in a state of evidence, and valid inferences are described in terms of operations that make us pass from grounds we already have to new grounds. Thanks to a rigorously developed proof- as-chains conception, the ground-theoretic framework permits Prawitz to overcome some conceptual difficulties of his earlier proof-theoretic explanation. Though from different points of view, anyway, the two accounts share an issue of recognizability of relevant operational prop- erties. Keywords Grounding - Inference - Operation - Proof - Recognizability Acknowledgments This work has been carried out thanks to the support of the A*MIDEX grant (n ANR-11-IDEX-0001-02) funded by the French Government “Investissements d’Avenir” program. 1 Introduction The notion of valid inference plays a fundamental role in mathematical logic. Despite of such an importance, the authors who have dealt with the topic differ from one another in several respects. There is no general agreement on what an inferences is, not to mention the question of which inferences are valid, and why they are so. In this debate, however, Dag Prawitz holds a prominent place, thanks to his well-known results in the discipline, as well as thanks to his original and deep insight into its main issues. From a very general point of view, an inference can be understood as an act of passage from some premises to a certain conclusion. Premises 1