Aquinas' Five Ways are five arguments proposed by the medieval philosopher Thomas Aquinas to demonstrate the existence of God. These arguments are based on observation of the world and aim to show that there must be a first cause or necessary being behind everything that exists. The Five Ways include the arguments from motion, causation, contingency, degrees of perfection, and design. Each argument builds on the idea that certain features of the universe, such as change and order, imply the existence of a higher power that initiated or sustains them.