According to St. Augustine and St. Thomas Aquinas, there is a natural human longing to find meaning and purpose in something greater than ourselves, like God. St. Thomas Aquinas provides five rational arguments for the existence of God: motion requires a prime mover, causation requires a first cause, contingency requires a necessary being, gradation requires an absolute being, and design requires a designer. While we can only speak of God analogously using human terms, mystery serves as a criterion of truth and answers the human quest for meaning.