  A key idea in Ibn Daud’s detailed description of the various functions of the vegetative, animal and rational faculties is the notion that there is a hierarchy of soul-faculties, in which the lower ones serve the higher. The speculative faculty of the human soul occupies the highest position in this hierarchy. Thanks to this faculty, which is directed towards the incorporeal world, man can perfect his knowledge and apprehend the incorporeal beings that are called angels in Scripture. It thus constitutes the link between man, angels and God. This faculty is served by the practical faculty, which is directed to the corporeal world, and governs man’s conduct. Although the soul is dependent on the body during the first stages of the acquisition of knowledge when the intellect passes from potentiality to actuality, it can exist separate from the body when it has attained the stage of acquired intellect. The rational soul is, therefore, immortal. According to Ibn Daud,