Prime matter, therefore, represents the first stage in creation. The next stage is the endowment of this formless matter with corporeality in the abstract, i. e., with extension. Then come the specific forms of the four elements, then their compounds through mineral, plant and animal to man. This is not new; we have already met with it in Gabirol and Ibn Zaddik. Nor is the following significant statement altogether new, though no one before Ibn Daud expressed it so clearly and so definitely. It is that the above analysis of natural objects into matter, universal body, the elements, and so on, is not a physical division but a logical. It does not mean that there was a time when prime matter actually existed as such before it received the form of corporeality, and then there existed actually an absolute body of pure extension until it received the four elements. No, nothing has existence in actu which has not individuality, including not only form, but also accidents. The above analysis is theoretical, and the order of priority is logical not real. In reality only the complete compound of matter and form (the individual) exists.
Allusion to matter and form is also found in the Bible in Jeremiah (18, 1ff.), "Arise and go down to the potter's house.... Then I went down to the potter's house, and, behold, he wrought his work on the wheels.... Behold as the clay in the potter's hand...."[233]
The next important topic analyzed by Ibn Daud is that of motion. This is of especial importance to Ibn Daud because upon it he bases a new proof of the existence of God, not heretofore found in the works of any of his predecessors. It is taken from Aristotle's Physics, probably from Avicenna's treatises on the subject, is then adopted by Maimonides, and through his example no doubt is made use of by Thomas Aquinas, the great Christian Scholastic of the thirteenth century, who gives it the most prominent place in his "Summa Contra Gentiles."
Ibn Daud does not give Aristotle's general definition of motion as the "actualization of the potential qua potential" (cf. above, p. [xxxii]), but his other remarks concerning it imply it. Motion, he says, is applied first to movement in place, and is then transferred to any change which is gradual, such as quantitative or qualitative change. Sudden change is not called motion. As the four elements have all the same matter and yet possess different motions—earth and water moving downward, fire and air upward—it cannot be the matter which is the cause of their motions. It must therefore be the forms, which are different in different things.
Nothing can move itself. While it is true that the form of a thing determines the kind of motion it shall have, it cannot in itself produce that motion, which can be caused only by an efficient cause from without. The case of animal motions may seem like a refutation of this view, but it is not really so. The soul and the body are two distinct principles in the animal; and it is the soul that moves the body. The reason why a thing cannot move itself is because the thing which is moved is potential with reference to that which the motion is intended to realize, whereas the thing causing the motion is actual with respect to the relation in question. If then a thing moved itself, it would be actual and potential at the same time and in the same relation, which is a contradiction. The Bible, too, hints at the idea that every motion must have a mover by the recurring questions concerning the origin of prophetic visions, of the existence of the earth, and so on. Such are the expressions in Job (38, 36, 37): "Who hath put wisdom in the inward parts?" "Who can number the clouds by wisdom?" In Proverbs (30, 4): "Who hath established all the ends of the earth?" and in many passages besides.[234]
The question of infinity is another topic of importance for proving the existence of God. We proceed as follows: An infinite line is an impossibility. For let the lines
be infinite in the directions b, d. Take away from cd a finite length = ce, and pull up the line ed so that e coincides with c. Now if ed is equal to ab, and cd was also equal to ab by hypothesis, it follows that ed = cd, which is impossible, for ed is a part of cd. If it is shorter than cd and yet is infinite, one infinite is shorter than another infinite, which is also impossible. The only alternative left is then that ed is finite. If then we add to it the finite part ce, the sum, ce + ed = cd, will be finite, and cd being equal to ab by hypothesis, ab is also finite. Hence there is no infinite line. If there is no infinite line, there is no infinite surface or infinite solid, for we could in that case draw in them infinite lines. Besides we can prove directly the impossibility of infinite surface and solid by the same methods we employed in line.
We can prove similarly that an infinite series of objects is also an impossibility. In other words, infinite number as an actuality is impossible because it is a contradiction in terms. A number of things means a known number; infinite means having no known number. A series is something that has beginning, middle and end. Infinite means being all middle. We have thus proved that an actual infinite is impossible, whether as extension or number. And the Bible also alludes to the finiteness of the universe in the words of Isaiah (40, 12): "Who hath measured the waters in the hollow of his hand ...," intimating that the universe is capable of being measured.
We must prove next that no finite body can have an infinite power. For let the line be a finite line having an infinite