In deducing the origin of things from their primary causes, Epicurus, however, deviates widely from his predecessor. Atoms—so it was taught by both—have by virtue of their weight been eternally engaged in a downward motion. [1176] That all bodies should move downwards in empty space seemed to Epicurus a matter of course; for whatever is heavy must fall unless it is supported. [1177] He was therefore opposed to the Aristotelian view that heaviness shows itself in the form of attraction towards a centre, and consequently to his further supposition that downward mode of motion belongs only to certain bodies, circular motion being for others more natural. [1178] The objection that in endless space there is no above or below he could meet only by appealing to experience; [1179] some things always appear above our heads, others beneath our feet. [1180] But whilst Democritus held that atoms in their downward motion meet together, thus giving rise to a rotatory motion, no such view commended itself to Epicurus. Nay rather in his view all atoms will fall equally fast, since empty space offers no resistance, and falling perpendicularly it is impossible to see how they can meet. [1181] To render a meeting possible he supposes the smallest possible swerving aside from the perpendicular line in falling. This assumption seemed to him indispensable, since it would be otherwise impossible to assert the freedom of the human will. For how can the will be free if everything falls according to the strict law of gravity? For the same reason this swerving aside was not supposed to proceed from any natural necessity, but simply from the power of self-motion in the atoms. [1182] In consequence of their meeting one part of the atoms rebounds—so Democritus also taught; the lighter ones are forced upwards, and from the upward and downward motions combined a rotatory motion arises. [1183] When this motion takes place a clustering of atoms is the consequence, which by their own motion separate themselves from the remaining mass, and form a world of themselves. [1184] Atoms being eternal and unchangeable, the process of forming worlds must go on without beginning or end; [1185] and inasmuch as they are also infinite in number, and empty space is infinite also, there must be an innumerable number of worlds. [1186] In the character of these worlds the greatest possible variety may be supposed, since it is most unlikely that the innumerable combinations of atoms all brought about at random will fall out alike. Equally impossible is it to assert that all these worlds are absolutely dissimilar. In general, Epicurus assumed that they are extremely different both in point of size and arrangement, and that here and there one may be similar to our own. [1187] Moreover, since eternity affords time for all imaginable combinations of atoms, nothing can ever be brought about now which has not already existed. [1188] In one respect all worlds are alike; they