Descartes incognito: La « préface » des Passions de l'âme

The matter of the two letters that, together with Descartes' replies, form the so-called "preface" to the Passions of the Soul (1649) has long haunted Cartesian scholars. Is this a real epistolary exchange or a small deception coming from Descartes himself? The fact that the so-called "preface" contains some philosophical positions that Descartes had never publicly exhibited before will offer, together with other pieces of historical evidence, a good argument in favor of the idea that he is the only author of this text.