Aristotle on the Motion of the Earth

The following is an essay I turned in for class. 

In On The Heavens Book II, Chapter 13 Aristotle states, “In general our quarrel with those who speak of the movements in this way cannot be confined to the parts, it concerns the whole universe.” (294b31 – 32) Explain what he means and how his criticism of his predecessors as well as his development of his own view illustrate what he means. (You will have to be selective in what you discuss here.)

The context in which Aristotle says this in his discussion about the underlying cause for the rest of the earth, that is to say, why the earth itself is not moving. This begins with his discussion of his predecessor's arguments that the earth is still because of its shape. Anaxagoras and Democritus reasoned that the earth is still because it is flat (294b15). The flat side which presents to the air is so wide that it doesn’t allow air to move around it, like a lid (294b15). And since movement through air is possible because one cuts through air, and cutting through isn’t possible with an object this large, the earth remains where it is at. Aristotle attacks this in a variety of ways. Firstly, he attacks the assumption that the earth is flat. Aristotle states that the flatness is not necessary for their theory to work, only that it is large enough. So, the theory about compressed air could still be true if the earth was spherical and large enough (294b25). Secondly, he states that the issue can be settled, not by looking at the parts of the earth, like it being flat, spherical, small or large, but rather by looking more broadly into whether bodies have a natural motion or not (294b30). So it looks more into the essential natures of the earth as a body rather than some accidental aspect of the earth like shape. It is in this context that Aristotle makes his statement in question. 

Aristotle then goes on to argue how such principles can settle the matter of the earth being stationary. Bodies have no natural or constrained, that is to say forced, movement (295a). It does not have an internal principle of motion, like animals do, nor is there anything in the universe which moves the earth by contact, like a bat hitting a ball. And since there is neither of these things, it would follow that there is no motion to earth (295a5). 

Aristotle also considers the view of Empedocles who argues that the speed of the motion of the heavens prevents movement of the earth like how one stirs water fast enough in a cup that you can see the bottom of the cup, even though the water naturally tends to the bottom. So likewise, even though the earth tends to fall, it is prevented by doing so because of the swirl of the heavens (295a20). Aristotle responds by presenting an internal difficulty for the view. If the elements are supposed to have been separated by hate, as Empedocles presumably does, then what caused the earth to not be separated as the rest of the universe is (295a30)? But surely there are distinctions between the elements, like light and heavy, before the whirl of the heavens began, so what accounts for that if the whirl of the heavens is supposed to account for it’s distinctions in the first place (295b5). So Emepdocles analysis of trying to explain the world via elements is found wanting.

Aristotle then considers the view of Anaximander who argues that since the world is related to the whole universe, and the earth wants to move in every direction in the universe, it remains still because it cannot view one direction more appropriate than the others (295b10-15). Aristotle responds that it would seem to prove too much, as for anything which were properly placed in the center would therefore have to stay there, which is evidently not true as we see fire in a proper middle place but then move. Again, Aristotle seeks to settle the question by appealing to general principles of motion and rest, and not on the particular makeup or constitution of the earth and its elements.