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On The Heavens   


to perceptible things is their nature. And there is also absurdity and

impossibility in the notion that the disorderly movement is infinitely

continued. For the nature of things is the nature which most of them

possess for most of the time. Thus their view brings them into the

contrary position that disorder is natural, and order or system

unnatural. But no natural fact can originate in chance. This is a

point which Anaxagoras seems to have thoroughly grasped; for he starts

his cosmogony from unmoved things. The others, it is true, make things

collect together somehow before they try to produce motion and

separation. But there is no sense in starting generation from an

original state in which bodies are separated and in movement. Hence

Empedocles begins after the process ruled by Love: for he could not

have constructed the heaven by building it up out of bodies in

separation, making them to combine by the power of Love, since our

world has its constituent elements in separation, and therefore

presupposes a previous state of unity and combination.

These arguments make it plain that every body has its natural

movement, which is not constrained or contrary to its nature. We go on

to show that there are certain bodies whose necessary impetus is

that of weight and lightness. Of necessity, we assert, they must move,

and a moved thing which has no natural impetus cannot move either

towards or away from the centre. Suppose a body A without weight,

and a body B endowed with weight. Suppose the weightless body to

move the distance CD, while B in the same time moves the distance

CE, which will be greater since the heavy thing must move further. Let

the heavy body then be divided in the proportion CE: CD (for there

is no reason why a part of B should not stand in this relation to

the whole). Now if the whole moves the whole distance CE, the part

must in the same time move the distance CD. A weightless body,

therefore, and one which has weight will move the same distance, which

is impossible. And the same argument would fit the case of

lightness. Again, a body which is in motion but has neither weight nor

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