Descartes has loaded the dice: if the meditating subject were to have pretended to be a madman, just as he was to pretend a moment later that he was dreaming, it would have been necessary to propose to him the tempting image of a madman believing in his madness that he is actually sitting here beside the fire, looking at his paper and taking himself for a man who is meditating about a man who is sitting here right now, beside the fire, etc.