The study of sleep and dreaming has broad implications for the status of the natural sciences among medieval scholars. Whether dreams were thought to arise from natural causes, and thus belong to psychology, or from supernatural causes, and thus belong to metaphysics, reflected a thinker's outlook on science and religion. In what follows I argue that the subject of sleep and dreams was one of the main areas of psychological inquiry and observation in the Middle Ages. Whether it was possible to acquire foreknowledge during sleep, and how, were crucial questions not only for believers in divine providence, but also for students of the mind's functions.

Some Jewish thinkers believed that dreams usually carry no message, but other philosophers, legal scholars, poets, and mystics expressed their belief that their own dreams were veridical. Reports of poetic inspiration or artistic creativity in dreams reflect intense interest in this possibility, taken for granted in much of the literature of the legalistic and kabbalistic “dream queries (šeʾelot ḥalom),” in which verbal information is sought through dreams. Even though biblical prophecy was assumed to be bestowed upon special people and to come from supernal sources, many viewed “the right to prophecy” through dreams as egalitarian rather than elitist: The science of the soul could explain predictive dreams as a natural psychological phenomenon, making them the common property of all human beings, regardless of religion, education, or physical constitution.