St. Thomas Aquinas recognized that there were some people who doubted the existence of God because, to them, logic did not allow for or explain God's existence. His way of motion is based on logic and the observation of things in nature, which can prove God's existence to those who could not accept or believe God on faith alone. He calls it the most obvious way. This first argument, the Argument from Motion, tries to prove the existence of God as the first mover, which is unmoved. Now, it is certain just by observing with the senses that some things in this world are in motion. Whatever is in motion, Aquinas states, is moved by something else. Aquinas then defines one type of motion as "nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality." Nothing can make this movement except by something that is already in the state of actuality. In the same respect the first object is in potentiality. For example, something cold like ice, can make water, which is potentially cold, which causes it to change and move. Now, it is impossible for the same thing to be in actuality and in potentiality at the same time. For instance, what is actually cold cannot simultaneously be potentially cold, though it may be potentially hot at the same time. So, it is impossible in the same reasoning that anything should be both the mover and thing being moved. In this, Aquinas means that nothing can move itself. Consequently, if something is in motion, it must have been put in motion by something else, which was put in motion by another and so on and so on. However, this cannot go on to infinity because there would never be an instance in which there was no first mover and, consequently, no subsequent movers. Objects being moved don't move by themselves. A bullet doesn't move by itself, its fired out of a gun.