The explanation of Ibn Daud--it was not original with him, as we have already seen the non-religious philosopher in Halevi's Cusari giving utterance to the same idea, and in Jewish philosophy Israeli touches on it--the explanation of Ibn Daud is grounded in his psychology, the Aristotelian psychology of Avicenna. The first degree of prophecy, he says, is found in true dreams, which happen to many people. Just as waking is a state of the body in which it uses the external as well as the internal senses, so sleeping is a state of the body in which the soul suppresses the external senses by putting them to sleep, and exercises its "natural" powers only, such as the beating of the heart pulse, respiration, and so on. The internal senses are also at work during sleep, or at least some of them. In particular the power of imagination is active when the external senses are at rest. It then makes various combinations and separations and brings them to the common sense. The result is a dream, true or false. When the senses are weak for one reason or another this power becomes active and, when not controlled by the reason, produces a great many erroneous visions and ideas, as in the delusions of the sick. The Deity and the angels and the Active Intellect have a knowledge of the past, present and future, and we already know that the soul, _i. e._, the rational soul, receives influence from the Active Intellect as a natural thing in every person. Now just as it gets from it science and general ideas, so it may receive a knowledge of hidden things if the soul is adequately prepared. The reason it cannot receive information of hidden things from the Active Intellect in its waking state, is because the soul is then busy in acquiring knowledge through the senses. In sleep, too, it may be prevented by the thick vapors rising from the food consumed during the day, or by anxiety due to want of food or drink. The imagination also sometimes hinders this process by the constant presentation of its foolish combinations to the common sense. But sometimes this power comes under the control of the reason, and then the rational soul is prepared to receive hidden things from the Active Intellect. In those cases the imagination transforms these facts into images, which are true dreams. If they concern an individual or a particular event, we do not call them prophecy, or at least the share of prophecy they may have is very small. We call them prophetic dreams when they concern important matters and have reference to a whole nation or nations, and come to pass in the distant future. An example of such a dream is that recorded in Daniel 7, 1.