first cause

In philosophy, an argument for the existence of God as creator or cause of the world. The First Cause argument – a version of the cosmological argument – turns on the idea that everything requires a cause or reason. God must exist to be the First Cause, because it is assumed either that an infinite regress of causes is impossible or that the existence of the universe itself needs explanation. For Aristotle, matter has always existed, so the First Cause, or Prime Mover as he calls God, is not the First Cause in time but the cause of the universe's continuing existence – a sustaining cause, or reason for its existence. For Thomas Aquinas, the first cause is both a sustaining cause of the world and the first cause in all the causal series that make up the world.