Early in meditations, Descartes says that no clear mark distinguishes dreaming from waking. "But in thinking over this, I remind myself that on many occasions, I have in sleep been deceived by similar illusions, and in dwelling carefully on this reflection I see no manifestly that there are no certain indications by which we may clearly distinguish wakefulness from sleep that I am lost in astonishment. An my astonishment is such that it is almost capable of persuading me that I now dream." (Descartes, 80). He worry's that since all we ever experience are our own inner mental states, we might, for all we could tell, be living in an illusion created by a malicious demon. In that case, most of our beliefs about reality would be false. Descartes' meditation's questions our definition of what reality is. Descartes states the dream argument and the evil genius scenario, both of which are intended to generate skeptical doubt. How do we know, for example, that we are awake now, rather than merely dreaming? How do we know that our thoughts are not being manipulated, and that our perceptions of 'reality' are accurate?
             What Descartes questions in his dream argument is that he often has perceptions very much like the ones he usually has in sensation while he is dreaming. Also, that there are no definite signs to distinguish dream experience from waking experience. Therefore it is possible that he would be dreaming right now and that all of his perceptions are false.
             Descartes realizes that someone may not accept that all of the elements of our dreams may be illusory, so he introduces the argument of the existence of God. Descartes states "And, besides, as I sometimes imagine that others deceive themselves in the things which they think they know best, how do I know that I am not deceived every time that I add two and three, or count the sides of a square, or judge of things yet simpler, if an...