Introduction to Astronomy

Finally, we subjoin to the philosopher's discourse that, since the circle moves, it is necessary to have a cause that moves it, which, if we do not understand, we will be led to infinity; but the motion of the circle is infinite, and therefore the moving virtue must be infinite, and thus infinite and incorporeal. Thus, therefore, it follows that the cause of all alteration and corruption is external.

A decorative drop cap 'Q' contains ornate scrollwork and floral motifs.

There are four genera, outside of which no species of things of the inferior world exists, which will be easily revealed when it is shown what the powers of the stars choose from the accidents of this world. These are: form, matter, composition, and the composite. Therefore, we shall use the manner of speaking among philosophers, by which they call the human form that which makes every individual of this species say 'this is a man,' and for a horse, 'this is a horse.' But matter or nature is fourfold: earth, water, air, fire. But composition is the harmony in the bodies of the elements. But the composite is that which escapes from a composition of this kind, such as are the bodies of all animals, sprouts, and metals. Therefore, in all bodies that we sense, these four genera are found: first, that which is composite; second, the composition; third, nature; fourth, the species. With these thus composed, we subjoin to the philosopher's discourse that every generated thing has a more ancient generator, and that the generated leads to the perception of existence; for example, the sustainer is more ancient than the sustained, as the earth is to terrestrial bodies. Thus, therefore, the compositions are then more ancient than the matter. Indeed, there will be genera and species of animals, sprouts, and metals in nature in potency, but finally in actuality as the composition succeeds. Nor is there composition unless there is something composing, and in whatever way it may be, so that the composite is not its own composer, nor is there matter for itself, which, since these things are so, it is necessary to have a generator; every generated thing and every composite thing has a composer discerning between the genera and species of all things. Hence, therefore, it is established that the creator is the generator, and then, by the movements of the stars, he has entrusted the guidance of nature. Indeed, it has been gathered from the aforementioned that the motion of the celestial is the virtue of such a composition and the cause of its difference; the sun is most powerful in the composition of individuals and in the differences of species, as it were, by the harmony specially reconciled of the soul and the body. Since, therefore, every composite consists of form and matter, the form nevertheless seeks for itself matter adapted to it, as if to the composites; whence in philosophy, the form is as the craftsman, but the matter is as the instruments. For just as different craftsmen work with their own instruments, needing nothing of another's—but the work is ascribed not to the instruments but to the craftsman—so too are the different forms; nor is this beast a bird, for what is adapted to the nature of man is alien to the beast. And thus one thing for the beast, another for the bird. For the human form assumes from the natures the hot and the humid, and thus from the rest, what is more subtle and apt for receiving the rational soul and the movements of standing, sitting, and the like, with an erect stature. But the form of the hot and dry, apt for claws, teeth, and beards, and for roughness, is the form of the beast; the cold and dry is suitable for hooves, claws, and legs. And thus every form draws what is congruent to itself from the passive matter. Thus, therefore, every composite is ascribed principally to the authority of the form, not of the matter.