Compendium of All Natural Science

proceed from the soul, they become animate. Natural motions are those which the elements and things composed of elements experience when the light tends upward and the heavy downward. Animate motions, however, are indifferent to every position of place. Those occur by force which are called compelled and involuntary, such as rotation, pushing, and carrying. But they differ among themselves in this way, as will become manifest to those who put it to the test. Natural motions indeed become gradually more intense toward their end, while compelled motions, on the contrary, become more slack; animate motions, however, are spurred on only in the middle.

25. On rest.

Since, indeed, there must be the same reasoning for contraries, it is most fitting that whatever we have said concerning motion can also be understood of rest by a different reasoning. It must be known that rest belongs to those things which, though they are capable of being moved, happen not to be moved. Wherefore, just as motion is contrary to motion, so rest is opposed to rest. Likewise, one kind of rest is natural, such as the ether in the heights; another animate, such as sitting; another compelled, such as fire at the lowest point. Likewise, whatever is at rest both has been at rest and will necessarily be at rest.

26. On place.

Since, indeed, it is necessary that everything which is moved have a place, for that reason those who discourse on motion must speak of place. Place, therefore, is that surface by which bodies are surrounded. Of itself, however, place is immobile. For the Moon is the place of fire, and water the place of the earth.