According to Aquinas, which way argues that nothing can be the cause of itself?

The Second Way, also known as the Causation of Existence, argues that nothing can be the cause of itself based on the principle of causality. Aquinas posits that everything that exists is the result of something else that brought it into existence. If something were to be the cause of itself, it would have to exist prior to its own existence, which is a contradiction. Thus, this leads to the conclusion that there cannot be an infinite regress of causes, and therefore, there must be a first cause that itself was not caused by anything else. This first cause is ultimately identified as God.

The other options focus on different aspects of Aquinas's arguments for God’s existence. The Argument from Motion centers on the idea that change requires a mover, while the Third Way deals with necessary and contingent beings. The Argument from Simplicity is not one of the classical five ways but rather emphasizes the need for a simple explanation of existence. Each of these concepts has its own unique angle, but it is the Second Way that specifically addresses the impossibility of self-causation.