The whole Universe is composed of substance and accidents; every substance must possess one accident or more, and since the accidents are not eternal, the substance, the substratum of the accidents, cannot be eternal; for that which is joined to transient things and cannot exist without them is itself transient. Therefore the whole Universe has had a beginning. To the objection, that the substance may possibly be eternal while the accidents, though in themselves transient, succeed each other in an infinite series, they reply that, in this case, an infinite number of transient things would be in existence, an eventuality which, according to their theory, is impossible. This argument is considered by them the best and safest, and has been accepted by many of them as a strict proof. Its acceptance implies the admission of the following three propositions, the object of which is well understood by philosophers. (1) An infinite series of things, of which the one succeeds when the other has ceased to exist, is impossible. (2) All accidents have a beginning.—Our opponent, who defends the theory of the eternity of the universe, can refute this proposition by pointing to one particular accident, namely to the circular motion of the sphere; for it is held by Aristotle that this circular motion is eternal, and, therefore, the spheres which perform this motion are, according to his opinion, likewise eternal. It is of no use to prove that all other accidents have a beginning; for our opponent does not deny this; he says that accidents may supervene an object which has existed from eternity, and may follow each other in rotation. He contents himself with maintaining that this particular accident, viz., circular motion, the motion of the heavenly sphere, is eternal, and does not belong to the class of transient accidents. It is therefore necessary to examine this accident by itself, and to prove that it is not eternal. (3) The next proposition which the author of this argument accepts is as follows: Every material object consists of substance and accidents, that is to say, of atoms and accidents in the sense in which the Mutakallemim use the term. But if a material object were held to be a combination of matter and form, as has been proved by our opponent, it would be necessary to demonstrate that the primal matter and the primal form are transient, and only then the proof of the creatio ex nihilo would be complete. The Fifth Argument.