I believe that nothing has ever existed of everything my lying memory tells me. I believe that body, shape, extension, motion, are functions. What is there then that can be taken as trueIJ Perhaps only this one thing, that nothing at all is certain. But I cannot forget that at other times, I have been deceived in sleep by similar illusions; and, I perceive so clearly that there exist no certain marks by which the state of waking can be distinguished from sleep. I am accustomed to, in my dreams, imagine the same things that lunatics imagine when awake.