The first way Aquinas attempts to prove the existence of God is through cause and effect. Every action or outcome must have a previous action that allowed that action or outcome to come about. This previous action must have been set in motion by another action. St. Thomas reasons that this infers an infinite chain of cause and effect, which would be impossible and there must be a starting point, a prime mover. This prime mover must be God according to St. Thomas.
Aquinas’ second argument is contingent existence and necessary existence. All natural bodies have an existence which is contingent upon something before them bringing them about. Like a baby being contingent upon its parents. This would go on forever like an infinite chain of dominoes which Aquinas says is impossible. There must be a necessary being upon whom all other being are contingent and owe their existence to. This being must be God.
The third way is based upon design qua regularity and how all beings without intelligence act with regularity. Aquinas uses the example of a formal garden, as plants lack intelligence they cannot decide how to grow and must be guided. As all the plants grow with regularity, a design or pattern, there must be something or someone guiding them towards an end, a gardener. Aquinas compares this to the universe, and how the universe moves with regularity, the earth orbiting the sun, and the moon orbiting the earth. Something must be guiding them as they cannot guide themselves.
Paley’s teleological argument differs to Aquinas’ in the form that Paley’s argument uses design qua purpose. His argument likens the universe to a machine and God being its designer.
Paley uses his watch analogy and expands it to the universe, saying that if one looks at the universe one can see that it is made up of an