This is an excerpt from the famous BBC Radio debate between Father Frederick C. Copleston and Bertrand Russell. In this section, they discuss Leibniz’s Argument from Contingency, which is a form of the Cosmological Argument. It differs from other Cosmological arguments (e.g. Kalam) in that it is consistent with an eternal universe, as it doesn’t appeal to first causes, but rather the principle of sufficient reason. It can be summarized in this way:
(1) Everything that exists contingently has a reason for its existence. (2) The universe exists contingently.
(3) The universe has a reason for its existence. (4) If the universe has a reason for its existence then that reason is God.