Thomas Aquinas offers two arguments for the existence of God, one from motion and one from causation, which are often referred to as the First Way and the Second Way, respectively. Both arguments are grounded in Aristotle's philosophy and rely on two fundamental principles: the principle of causality and the principle of non-contradiction.The First Way argues from motion, which is understood broadly as any kind of change. Aquinas begins by observing that things in the world are constantly in motion and that nothing can move itself. He reasons that for any object to be moved, something else must move it. But if we trace this chain of motion back, we arrive at the conclusion that there must be a first mover, which itself is not moved by anything else. Aquinas argues that this first mover must be God, who is the source of all motion in the universe.The Aristotelian claim that underpins the First Way is that "everything that is moved is moved by another." This means that nothing can move itself, and that every change requires a cause outside of itself. In other words, motion is always caused by something else, and there can be no uncaused motion.The Second Way argues from causation, specifically from the idea of efficient causation, which is the process by which a cause brings about an effect. Aquinas begins by noting that everything in the world has a cause, and that no cause can cause itself. He reasons that for any cause to exist, there must be a first cause that set the chain of causation in motion. This first cause must itself be uncaused, or else we would have an infinite regress of causes, which Aquinas argues is impossible.The Aristotelian claim that underpins the Second Way is that "it is not possible to proceed to infinity." This means that there must be a first cause, and that there cannot be an infinite chain of causes stretching backwards in time. This is because an infinite regress of causes would mean that there is no ultimate cause or explanation for why things exist, which Aquinas finds unacceptable.Both the First Way and the Second Way rely on the principle of causality, which states that every effect has a cause. They also rely on the principle of non-contradiction, which states that something cannot both be and not be at the same time and in the same respect. For Aquinas, these principles point to the existence of God as the ultimate cause and explanation for why things exist and change in the world