The extreme imaginative richness of dreaming means that, from the point of view of logic and reasoning, the experience of the dream will be, in order to doubt the totality of the sensibledomain, at least as convincing as madness; but the fact that it can happen to me enables it to enter the very movement of the meditation, and to become a test in its own right, and an effective one, whereas madness is an experience that is immediately impossible.