Various possibilities, that one is dreaming, that one is being deceived by a deceitful demon, that one is a brain in the vat being stimulated to think one has a body and is in a regular world, have been invoked to show that all one's experience-based beliefs might be false. Descartes in Meditation I advises that in order not to lapse into his careless everyday view of things he, or at least his meditator, should pretend that all his experience-based beliefs, (...) indeed all his …. (shrink)