In the eighteenth century the question of whether the order and complexity in the universe (revealed in ever more astonishing detail by scientists during the Enlightenment) could really be taken to imply purpose and a divine designer was central to many philosophers’ thinking. Hume was an empiricist. He rejected any attempt to prove God’s existence through a priori reasoning and the Ontological Argument. He believed that statements which did not refer to verifiable states of affairs were meaningless. He was not convinced by inductive attempts to prove God’s existence either. However, in Hume’s day professing atheism and even expressing doubt about the grounds for believing in God, was not popular! Therefore Hume kept his views on religion relatively quiet and the most he said publically was that he was an agnostic. He wrote most of Dialogues concerning natural religion in and shortly after 1750, but they were not published until after his death.
The book takes the form of a dialogue between three characters in the manner of Cicero. Pamphilus is a youth present during the dialogues. He serves as the narrator and at the end he loyally, perhaps ironically, suggests that Cleanthes, his teacher, offered the strongest arguments. Cleanthes bases his beliefs about God's existence and nature upon a version of the teleological argument, which uses evidence of design in the universe to argue for God's existence and resemblance to the human mind. Philo, probably represents a viewpoint similar to Hume's own. Philo and Demea attack Cleanthes' teleology and suggested anthropic argument. While not going as far as to deny the existence of God, Philo asserts that human reason is wholly inadequate to make any assumptions about the divine.
Demea defends philosophical theism. He believes that the existence of God should be proven through a priori reasoning and that our beliefs about the nature of God should be based upon revelation and faith. Demea rejects Cleanthes' natural religion (faith based on inductive reasoning) for making man the measure of all things. Demea objects to the abandonment of the a priori arguments by Philo and Cleanthes (both of whom are empiricists). Cleanthes, summarizing the teleological argument, likens the universe to a man-made machine, and concludes by the principle that similar effects have similar causes, it must have a designer. Philo is not satisfied with the teleological argument. He attempts a number of criticisms and makes the point that if God is the designer of the Universe, then assuming divine characteristics such as omnipotence and omniscience is not justified. He jokes that far from being the perfect creation of a perfect designer, this universe may be "only the first rude essay of some infant deity ... the object of derision to his superiors."