Philosophical arguments for the existence of God are fun, but they really only back up what I already know from experience, they are not the sole reason why I believe. That said, the cosmological argument is cool !

The basic premise of all of these is that something caused the Universe to exist, and this First Cause must be God. It has been used by various theologians and philosophers over the centuries, from the ancient Greek Plato and Aristotle to the medieval St. Thomas Aquinas and the 20th century Frederick Copleston.