The later philosophers assumed ten Intelligences, because they counted the spheres containing stars and the all-encompassing sphere, although some of the spheres included several distinct orbits. There are altogether nine spheres, viz., the all-encompassing sphere, that of the fixed stars, and those of the seven planets; nine Intelligences correspond to the nine spheres; the tenth Intelligence is the Active Intellect. The existence of the latter is proved by the transition of our intellect from a state of potentiality to that of actuality, and by the same transition in the case of the forms of all transient beings. For whatever passes from potentiality into actuality, requires for that transition an external agent of the same kind as itself. Thus the builder does not build the storehouse in his capacity of workman, but in that of a person that has the form of the storehouse in his mind; and that form of the building which exists in the mind of the builder caused the transition of the potential form of the storehouse into actuality, and impressed it on the material of the building. As that which gives form to matter must itself be pure form, so the source of intellect must itself be pure intellect, and this source is the Active Intellect. The relation of the latter to the elements and their compounds is the same as that of the Intelligences to their respective spheres; and our intellect in action, which originates in the Active Intellect, and enables us to comprehend that intellect, finds a parallel in the intellect of each of the spheres which originates in the Intelligence corresponding to that sphere, and enables the sphere to comprehend that Intelligence, to form an idea of it, and to move in seeking to become similar to it.