This, however, explains but a portion of the phenomenon. Even if it be a true solution, it accounts only for the acceptance in dream of the ideal as real. It leaves wholly unexplained the more remarkable feature exhibited in the entire unconsciousness by the dreamer of the absurdities and impossibilities presented in the dream and the absence of surprise and wonder how such things can be. In the waking state, the mind would therefore reject them instantly as the illusions they are. Hence the reasonable conclusion that, in addition to the sleep of the senses and of the _will_, some part of the material mechanism of the mind is also sleeping or its activity is suspended during dream. The investigation is of serious moment, for it raises some other questions of even greater importance. If the explanation be sufficient, it determines some moot points in Mental Physiology. It proves that the mental machine, the brain, is _not_ one and indivisible—that the _whole_ brain is not employed in each mental act, as contended by Dr. CARPENTER. To what mental faculties are we indebted for our waking consciousness of incongruity, impracticability, absurdity, irrationality? Obviously these faculties must be slumbering in dream. To _their_ temporary paralysis this most remarkable phenomenon of dream is certainly due. The popular notion is that _reason_ is the slumbering faculty. We talk of reason as being the special attribute of Man. In fact there is no such faculty. There is a mental process we call reasoning; but it is performed by the joint action of various mental faculties. One presents the things to be reasoned upon; another compares them and presents their resemblances and differences; a third enables us, by the process we call _reasoning_, to apply these resemblances and differences to some third subject and thus from the known to predicate the unknown. It is familiar to every reader that this process of reasoning is not always suspended in dream. On the contrary, it is sometimes abnormally active. We reason rightly often, but on wrong premisses. What we are unable to discover in dream is the unreality of the subject matter upon which we are reasoning. If, for instance, you dream that you are making a speech or preaching a sermon. In your dream you pursue a logical argument, but you found it upon imagined facts that are untrue and improbable, which the waking mind would not entertain for a moment, but which in your dream you accept as true and implicitly believe to be real. We shall, perhaps, arrive at the solution of this problem by the process of exhaustion.