C. Mossner, author of the definitive modern biography of Hume and editor of the Penguin Classics edition of the Treatise, has written:

The Dialogues concerning Natural Religion, as an example of the philosophical dialogue, is beyond dispute the most brilliant in the English language, surpassing Berkeley’s Three Dialogues between Hylas and Philonous (1713), the only serious contender… The Dialogues is the final marriage of philosophy with art that had been Hume’s ambition throughout a long career as man of letters.3

Here we shall consider some of the main philosophical ideas they contain, and then look briefly at the literary style they exemplify, bearing in mind Mossner’s comment, for the marriage of philosophy and art Hume achieves prevents us from interpreting them in a way that divorces content from style and structure.

The Dialogues are ostensibly a written record made by a young man, Pamphilus, of a conversation between three characters, Cleanthes, Demea and Philo. Pamphilus, whose education is being supervised by Cleanthes, sends the account, with an introductory section and occasional interposed remarks of his own, to a friend, Hermippus. The Greek names of the characters, and the style and topics, show that Hume is adopting the technique of modelling his work on a classical original, in this case Marcus Tullius Cicero’s De Natura Deorum (On the Nature of the Gods). Cicero examined in dialogue form the three main theologies then prevalent, the Epicurean, the Stoic and the Academic. Similarly, different conceptions of theology and the nature of religious belief are presented in Hume’s work, and examined dialectically. The work is divided into twelve parts.

The first half of the eighteenth century was a period of intense debate in theology. One element was the writings of a group of thinkers known as deists. Deism was not a sharply defined position, but roughly it consisted of the view that all that it is necessary to believe in religion is what can be established about God, his purposes, and man’s religious duty, by reason alone. Christian theologians had always drawn a distinction at some point between natural and revealed religion, that is, between what can be known of God by rational argument and what is to be accepted by faith as the special revelation of God in Christ. Faith was understood to be a response to truths revealed through the working of the Holy Spirit made possible by grace, a spiritual gift from God. However, it was also held that at least the existence of God, his nature as supreme creator, infinitely wise, powerful and benevolent, and his will that constitutes the moral law, could be known without revelation. And it was also common to hold that there can be evidence, acceptable to reason, that some religious teaching is part of God’s revelation. Such things as the occurrence of miracles and the fulfilling of prophecies could be cited as evidence of Christ’s divinity or of the inspiration and guidance of the church by the Holy Spirit. Scriptural authority for both the possibility of rational knowledge of God and for the necessity for salvation of the spiritual response of faith, could be found in St Paul. Almost universally, theologians cited The Epistle to the Romans, chapter 1, in support of the possibility of natural knowledge of God, and The First Epistle to the Corinthians, chapter 2, for the necessity of a spiritual response of faith.

Some deists rejected altogether the need for revelation and faith. Edward Herbert (1583–1648) in De Veritate (On Truth, 1624) had rejected the ideas of non-rational faith, an infallible church and the authority of priests as no part of ‘true religion’. For him, true religion, purged of superstition, was a wholly rational affair consisting in an acceptance of ‘common notions’ that all men have. These are, that there is one supreme God; that he ought to be worshipped; that virtue and piety are the essence of worship; that we ought to be sorry for our sins and repent; and that God’s goodness consists in his rewarding virtue and punishing vice in this world and the next. There is nothing especially Christian in Herbert’s ‘true religion’, and he made an attempt, in De Religione Gentilium (On the Religion of the Gentiles, 1663) to show by a comparative discussion of ancient religions that all men at all times have accepted these beliefs.

Other deists hoped to show that Christianity, when properly understood, is also a wholly rational religion. They relied heavily upon reasoned argument, and drew some inspiration from the new science of Sir Isaac Newton (1642–1727) and Robert Boyle (1627–91). Arguments to prove the existence of God by appeal to the evidence of his ‘general providence’ displayed in the order of nature, and by more traditional reasoning based on the idea of God as a self-existent or necessary being, can be found in such works as Christianity not Mysterious (1696) by John Tolland (1670–1722), and Christianity as Old as the Creation (1731) by Matthew Tindal (1655–1733).

Many deists, then, held that religion is originally a rational response to the evidence of God’s existence and providence displayed in nature, and that religious cults, rituals and mysteries, taking many forms and with proliferations of creeds, are all corruptions of the one true natural religion. Deism in this form was, in Hume’s opinion, wholly mistaken. In The Natural History of Religion he argues against Herbert’s attempt to show an original, rational monotheism at the base of all religions. The idea of divine providence, he says, does not in fact originate in a rational, detached admiration for the beauty and order of nature. Rather, religion originates in our emotional responses to the uncertainties of life, in our feelings of insecurity and vulnerability in a hostile world. Admiration of the regularity of the motion of the planets and appreciation of the divine wisdom increased by the discoveries of Galileo, Copernicus and Newton is not the common state of men’s minds. Although the wise, who are concerned with theoretical explanation, may be led to the idea of a single supreme creator, the vulgar, ordinary men and women, are moved by

… the ordinary affections of human life; the anxious concern for happiness, the dread of future misery, the terror of death, the thirst for revenge, the appetite for food and other necessaries. Agitated by hopes and fears of this nature, especially the latter, men scrutinize, with a trembling curiosity, the course of future causes, and examine the various and contrary events of human life. And in this disordered scene, with eyes still more disordered and astonished, they see the first obscure traces of divinity.4

The contrast is between admiration of regularity and order on the one hand, and fear and anxiety in face of disorder on the other.