MOVEMENT IS SAID TO BE MEASURED BY SPACE, BECAUSE OF ITS INDETERMINATION.
The measure of movement, therefore, seems to be what is measured by a definite movement, but which is other than this movement. There is a difference, indeed, between that which is measured, and that which measures; but that which is measured is measured only by accident. That would amount to saying that what is measured by a foot-rule is an extension, without defining what extension in itself is. In the same way, because of the inability to define movement more clearly because of its indeterminate nature, we say that movement is that which is measured by space; for, by observation of the space traversed by movement, we can judge of the quantity of the movement.