“Larvatus prodeo,” “I go forth masked”: with these words does the young René Descartes - the year is 1619 and he is twenty-three years old - mark his entrance into philosophy. In an early text found among his papers and published under the title Praeambula, he writes the following: “Before going on stage, an actor dons a mask (persona) so as not to reveal the redness of his face. Likewise, as I make my appearance in the theater of the world, where I have so far been only a spectator, I also go forth masked.”

Here Descartes describes a practice that is far from his alone. When a philosopher appears upon the stage – whether in speech or in writing – he alters his tone and projects his voice. He no longer merely speaks; he declaims, and sometimes even takes an oracular stance. He uses the mask to hide his face and body and above all to transform his voice. What we hear is the voice of René Descartes, but it is transformed, amplified, deformed by the mask behind which he hides, by the persona of the philosopher he wants to be. These few lines of the Praeambula may be considered as a beginning, a very personal preface to his philosophical oeuvre as a whole, as the moment when he leaves behind his person to become a persona. Until now, Descartes has been a private person, answerable to no one, able to express himself just as he is, just as he thinks he is, without having to use a mask. Once he openly, officially chooses the life of the mind, a new “I'” is expressed through his mouth; from now on what he says will no longer be private but public. His role now is to speak the truth, even if it turns out in the end to be his truth alone.