A History of Western Philosophy: And Its Connection with Political and Social Circumstances from the Earliest Times to the Present Day

by Bertrand Russell

The existence of God is proved, as in Aristotle, by the argument of the unmoved mover.II There are things which are only moved, and other things which both move and are moved. Whatever is moved is moved by something, and, since an endless regress is impossible, we must arrive somewhere at something which moves without being moved. This unmoved mover is God. It might be objected that this argument involves the eternity of movement, which Catholics reject. This would be an error: it is valid on the hypothesis of the eternity of movement, but is only strengthened by the opposite hypothesis, which involves a beginning, and therefore a First Cause.