The world according to Descartes is a prison. A potentially malign dream-giving-instance is playing a seemingly interactive movie to the victim of the dream. Is there an escape button? Descartes himself saw a way — intra-dream consistency. As long as unfalsified it enables the illusion of one's being even. For there are "hostages' in the dream relative to whom one is exterior and hence infinitely powerful. The risk that one refrains from misusing this power could not have been taken by a malign demiurge. This ethical argument makes rationalism so precious. Can classical rationalism be saved in the face of quantum mechanics? The proposed trick is classical endophysics — to posit two levels of objective reality (exo and endo). The interface (endo-reality) is the formal analogue of the big dream. Five predictions concerning empirical physical reality suggest themselves (stochastic noise, nonlocality, double nonlocality, rotational-frame covariance, nowness tunneling). A refined test of rationalism becomes possible.