Philosophical Context for Dialogues Concerning Natural Religion
Hume's skepticism was the result of more than his strong commitment to the Enlightenment ideal of the supremacy of reason; it was also largely the result of his equally strong commitment to the philosophical principles of British Empiricism. Following in the footsteps of George Berkeley, Hume believed that all factual knowledge derives from experience. In contrast to the rationalists, such as René Descartes and Nicolas Malebranche (both influential for Hume), who believed that knowledge of matters of fact can be attained through the use of our reasoning faculty, Hume maintained that all matters of fact are established solely on the basis of our experience of the world. (In other words, according to Hume, you cannot just sit in your armchair, think really hard, and expect to come up with any knowledge of matters of fact. In order to arrive at new substantive knowledge, you have to go out into the world and investigate.)
In exploring the possibilities of human knowledge—whether it be scientific knowledge, moral knowledge, or religious knowledge—the relevant question for Hume was always the same: does our experience of the world provide us with enough evidence to draw a rational inference to the relevant conclusions? If experience does provide us with enough evidence, then the relevant beliefs (e.g. religious belief, in the case of Dialogues Concerning Natural Religion) are justified and so rational, and if experience does not provide us with enough evidence, then the relevant beliefs are not justified and so not rational. (The assertion that a claim is rational if and only if it is supported by the evidence is commonly referred to as evidentialism. Both empiricists and rationalists alike believed firmly in evidentialism.)
Hume's commitment to empiricism accounts for the narrow focus of his religious investigation in the Dialogues. It might seem arbitrary, given the variety of arguments for God's existence that were employed in Hume's day, for him to have focused almost exclusively on one such argument, the argument from design. It is true that this particular argument (which claims that the intricate order and beauty of our universe is proof of an intelligent and benevolent designer) was enjoying a particular vogue during this period, largely because it was espoused by Sir Isaac Newton, but there were also other fashionable arguments, such as the ontological argument (which sought to prove God's existence from His very nature) and the cosmological argument (which claimed that God had to exist in order to account for our existence). Hume's focus makes sense when we consider that the argument from design is the only one of the three that seeks to base its conclusions on evidence drawn from experience of the world. Only the argument from design looks to the world and asks, "is there enough evidence here to justify our belief in an infinitely good, wise, and omnipotent God?"
In engaging in his investigation of religious belief, Hume was engaging three types of 18th century thinkers, each of whom is represented by a character in the dialogue. First of all, he discusses sort of man who would believe in the argument from design, the empirical theist. The empirical theist believes that by looking at the world, we can come to knowledge about both the existence and the nature of God. The most famous empirical theist of Hume's day was Sir Isaac Newton, but there were also other prominent defenders of the position such as the Dutch scientist and theologian Bernard Nieuwentyt. The second type of man that Hume discusses in this dialogue is the orthodox Christian or fideist, who believes that because human intellectual resources are too weak to lead us to any certain truths, we should abandon reason and accept truths on faith. Famous fideists include Montaigne and Pascal. Finally, Hume presents the skeptic, who is not wholly satisfied with either of these alternatives.
It is in part a testament to Hume's fair and thorough treatment of all these positions that followers of all three of these philosophical traditions have claimed Hume as their greatest mouthpiece. It is almost certainly the religious skeptics who have the best case for calling Hume one of their own (he incontrovertibly set the model for all later attacks on the rationality of religious belief), but fideists have been nearly as adamant in declaring him the greatest voice defending religious orthodoxy. The German philosopher J.G Hamann, for instance, was convinced that Hume had provided the most cogent argument for fideism by proving that there was no rational evidence for Christianity. He translated the dialogues into German hoping that Immanual Kant would read them and become a serious Christian. The Danish theologian Søren Kierkegaard, the most important Christian fideist of the nineteenth century, was also very impressed by this interpretation of Hume's position.