On August 10, 1787, Thomas Jefferson wrote a letter to his nephew Peter Carr in which he summarized the critical attitude toward revealed religion that typified the viewpoint of deists and other freethinkers of Jefferson’s day. After advising Peter to “shake off all the fears and servile prejudices, under which weak minds are servilely couched,” Jefferson continued:

Fix reason firmly in her seat, and call to her tribunal every fact, every opinion. Question with boldness even the existence of God; because, if there be one, he must more approve of the homage of reason, than that of blindfold fear.

This was a common deistic sentiment. If God created man with the faculty of reason, then surely he intended us to use that ability to the fullest extent possible. Of course, reason is a fallible instrument, so we are bound to make mistakes; nevertheless, it is morally better to make an honest error of judgment than to submit passively to the dictates of a religious creed because we fear the consequences of error. Deists tended to view God as a freethinker writ large. As a rational and benevolent being who endowed humans with the ability to reason so they could reach independent judgments, God would never punish his creatures for making honest mistakes—so we have nothing to fear from reasoning to the best of our ability, even if we happen to be wrong. Jefferson wrote:

You will naturally examine first, the religion of your own country. Read the Bible, then, as you would read Livy or Tacitus. The facts which are within the ordinary course of nature, you will believe on the authority of the writer, as you do those of the same kind in Livy and Tacitus. The testimony of the writer weighs in their favor, in one scale and their not being against the laws of nature, does not weigh against them. But those facts in the Bible which contradict the laws of nature, must be examined with more care, and under a variety of faces. Here you must recur to the pretensions of the writer to inspiration from God. Examine upon what evidence his pretensions are founded, and whether that evidence is so strong, as that its falsehood would be more improbable than a change in the laws of nature, which he relates.

Jefferson cited the famous story in the Book of Joshua (10: 12-13) in which God supposedly made the Sun stand still “for about a whole day” so the Israelites would have the daylight necessary to complete their slaughter of a retreating enemy. We would not believe that story if it had been related by Livy or Tacitus, but many people accept the story because they believe “that the writer of that book was inspired.” So Jefferson advised Peter to pursue the matter further and “examine, candidly, what evidence there is of his having been inspired.” Is it credible that, contrary to the laws of nature, “a body revolving on its axis, as the earth does, should have stopped, should not, by that sudden stoppage, have prostrated animals, trees, buildings, and should after a certain time have resumed its revolution, and that without a second general prostration[?] Is this arrest of the earth’s motion, or the evidence which affirms it, most within the law of probabilities?”

By the time Jefferson wrote this letter, his argument against miracles (and supernatural events generally), based on an assessment of the probabilities of competing explanations, had been around for a long time and was commonly found in the writings of deists and other freethinkers. It predated by many years even the classic formulation by David Hume. One of the most influential early formulations appears in Leviathan (1651, Chapter 32), by Thomas Hobbes. Suppose a man says that God spoke to him in a dream. According to Hobbes, this is

no more than to say he dreamed that God spake to him; which is not of force to win belief from any man, that knows dreams are for the most part natural, and may proceed from former thoughts; and such dreams as that, from self-conceit and foolish arrogance, and false opinions of a man’s own godliness, or other virtue, by which he thinks he hath merited the favour of extraordinary revelation. To say he hath seen a vision, or heard a voice, is to say, that he hath dreamed between sleeping and waking: for in such manner a man doth many times naturally take his dream for a vision, as not having observed his own slumbering. To say he speaks by supernatural inspiration, is to say he finds an ardent desire to speak, or some strong opinion of himself, for which he can allege no natural and sufficient reason. So that though God almighty can speak to a man by dreams, visions, voice, and inspiration; yet he obliges no man to believe he hath so done to him that pretends it; who, being a man, may err, and, which is more, may lie.

The sustained skeptical attack on historical miracles, which progressed throughout the eighteenth century, profoundly influenced how histories were written. Even when the deist Edward Gibbon published the first volume of The Decline and Fall of the Roman Empire in 1776, it was still common to attribute the success of early Christianity to divine favor, or “providence.” It is therefore no surprise that chapters 15 and 16 of Gibbon’s great work unleashed a torrent of criticism from the orthodox, for Gibbon resolved to explain the history of early Christianity by purely naturalistic means. And Gibbon, in his brilliantly ironic style, made it clear that legitimate history must preclude any and all appeals to miraculous events. If the historian substitutes miracles for explanations based on natural causation, then all bets are off, as history degenerates into fabulous stories of supernatural forces that defy human understanding.

According to Gibbon, every historian who attempts to write a reliable account of early Christianity must confront the uncomfortable fact that the “scanty and suspicious materials of ecclesiastical history seldom enable us to dispel the dark cloud that hangs over the first age of the church.”

The theologian may indulge the pleasing task of describing Religion as she descended from Heaven, arrayed in her native purity. A more melancholy duty is imposed on the historian. He must discover the inevitable mixture of error and corruption which she contracted in a long residence upon earth, among a weak and degenerate race of beings.

How did Christianity come to dominate a large segment of the civilized world? A traditional answer was that this success “was owing to the convincing evidence of the doctrine itself, and to the ruling Providence of its great Author.” History, however, is never that simple.

But as truth and reason seldom find so favourable a reception in the world, and as the wisdom of Providence frequently condescends to use the passions of the human heart, and as the general circumstances of mankind, as instruments to execute its purpose, we may still be permitted, though with becoming submission, to ask, not indeed what were the first, but what were the secondary causes of the rapid growth of the Christian church?

Among the five fundamental causes to which Gibbon attributed the eventual triumph of Christianity, it was mainly his discussion of the third—“The miraculous powers ascribed to the primitive Church”—that generated the maelstrom of controversy, for Gibbon made it clear that he did not take those reported miracles seriously.  

Gibbon noted that reports of early Christian miracles “have been lately attacked in a very free and ingenious inquiry, which, though it has met with the most favorable reception from the public, appears to have excited a general scandal among the divines of our own as well as of the other Protestant churches of Europe.” We might suppose that Gibbon was here referring to David Hume’s An Enquiry Concerning Human Understanding (1748), in which Hume repudiated all historical accounts of miracles; but Gibbon was actually thinking of a work by the Christian clergyman and scholar Conyers Middleton, Free Inquiry into the Miraculous Powers, which are Supposed to have Subsisted in the Christian Church (1749). This book, though largely forgotten today, was more widely read in the mid-eighteenth century than Hume’s account, and it generated more controversy. Indeed, it was Middleton’s book that caused a young Edward Gibbon to lose what remained of his faith in Christianity.

Middleton supposedly wrote his Free Inquiry to defend Protestantism against Catholicism. (The qualifier “supposedly” is sometimes necessary when discussing works of this kind, for rationalistic Christians sometimes joined deists in the practice of literary subterfuge.) Protestants and Catholics alike believed that miracles were a certain sign of divine favor, so Protestants needed to explain—or, more precisely, explain away—the many miracles reported by Catholics for centuries after the death of Jesus. The standard Protestant explanation was that miracles had declined precipitously after the apostolic age (roughly, 33-100), but in fact, as Middleton pointed out, miracles reported by Catholics remained extremely common “from the earliest father who first mentions them down to the time of the Reformation.” Something was clearly amiss here, for was not the Catholic Church, as viewed by Martin Luther and other Protestant Reformers, the Antichrist and the Whore of Babylon? So how could the wicked Catholic Church possibly be the beneficiary of divine miracles?

Middleton sought to resolve this dilemma by focusing primarily on Church Fathers from the fourth century. He accused them of outright lying, of forging documents, of falsifying history, and of manufacturing other pious frauds—all in the name of winning converts to Christianity. If ever an argument exemplified the inner logic of ideas, this was it, for the question naturally arose (at least to skeptics): If miracles reported by early Church Fathers lacked credibility, then why wouldn’t similar arguments apply to the miracles attributed to Jesus in the Gospels? Although Gibbon did not press his argument this far, at least not explicitly, it is not difficult to understand why his application of Middleton’s critique outraged many of his orthodox readers.

According to Gibbon, our beliefs about early Christianity will be determined not so much by the arguments advanced for this or that particular miracle, but chiefly by “the degree of the evidence which we have accustomed ourselves to require for the proof of a miraculous event.” Although the historian should not allow his religious convictions to warp his historical judgment, he must nevertheless work from a theory, whether implicit or explicit, of the relative probability of historical miracles, and then apply that theory to the particular case of early Christianity.

Gibbon, like Middleton, noted that miracles had been reported by many Christians from the earliest days of Christianity through many centuries thereafter, including the eighteenth century. Yet the Protestants of Gibbon’s day, while persuaded of the authenticity of early miracles, were far more skeptical of later reports—especially when those reports came from Catholics—often rejecting them outright. But how can we draw a rational line between true and false reports, between authentic miracles and superstitious fables? It was while focusing on this question that Gibbon made his most telling critique of historical miracles.

Reports of miraculous cures, which were commonplace in the early Christian community, were cited by Church Fathers as evidence for the truth of Christianity. But those mundane miracles should not surprise us, Gibbon argued, when we consider that “about the end of the second century, the resurrection of the dead was very far from being esteemed an uncommon event; that the miracle was frequently performed on necessary occasions…and that the persons thus restored to their prayers had lived afterwards among [Christians] many years.” What is the historian to make of such reports? Given the frequency of reported resurrections during the second century, and given the easy availability of those former corpses who were now up and about and ready to testify for their faith, Gibbon wondered why early Christians did not convince many more people than they actually did. How could anyone remain skeptical about a solitary resurrection in the past (that of Jesus) when he could easily observe or otherwise verify many such resurrections in the present? Moreover, how are we to understand the curious response given by Theophilus (Bishop of Antioch) to a skeptical friend? That skeptic promised to embrace Christianity immediately upon meeting just one former corpse, but as Gibbon observed: “It is somewhat remarkable that the prelate of the first eastern church, however anxious for the conversion of his friend, thought proper to decline this fair and remarkable challenge.”

Consider, observed Gibbon, that every age has its share of reported miracles, “and its testimony appears no less weighty and respectable than that of the preceding generation.” How then are we to avoid inconsistency if we deny the Christian miracles of, say, the eighth or twelfth centuries while accepting those in the second century? There is no appreciable difference from one age to the next in the number of witnesses or in their characters, so all such miraculous accounts, in whatever era we find them, have an equal claim to our assent. Nor is there any difference in the usefulness of such miracles, for “every age had unbelievers to convince, heretics to confute, and idolatrous nations to convert; and sufficient motives might always be produced to justify the interposition of heaven.”

Despite these similarities, even most friends of divine intervention believed that there was some period in which miracles were “either suddenly or gradually withdrawn from the Christian church.” Here Gibbon was thinking primarily of Protestants—those who affirmed the veracity of miracles during the apostolic age, using them to corroborate their own religion, while repudiating later claims of miraculous events authenticated by the despised Catholic Church.

Whatever time is chosen as marking the dividing line between authentic and bogus miracles, Gibbon called it a “just matter of surprise” that the Christians who lived during that transition period were quite unaware of the dramatic change that was taking place. Those Christians who previously had been endowed with sufficient faith to discern authentic miracles were suddenly unable to distinguish between true and false accounts, as if their faith had insensibly degenerated into superstitious credulity. Those Christians, after all, claimed to have witnessed miracles firsthand, just as they always had; and if we accept their earlier accounts (i.e., before the transition to bogus reports) as genuine, then we must suppose them to have been of sufficient discernment to recognize the marks of authentic miracles. As Gibbon put it: “The recent experience of genuine miracles should have instructed the Christian world in the ways of Providence and habituated their eye…to the style of the divine artist.” But if this were so, then how did those discerning Christians lose this ability after the transition period and suddenly begin to defend bogus miracles with the same assurance, and using the same kind of evidence, with which they had previously confirmed authentic miracles?

Gibbon, in effect, was posing the following question: Which is more likely—that experienced, honest, and credible witnesses should suddenly and unaccountably become deceitful, unreliable, and superstitious? Or that all such accounts were unreliable from the outset, and should not be accepted by the historian as grounds for accepting any historical reports of miracles? Gibbon left no doubt about his answer. The skeptical analysis of miracles—one defended by virtually every deist of the eighteenth century—had taken its toll, as purely secular histories became the rule rather than the exception. Although Edward Gibbon was not the first modern historian to adopt this approach—we also find it in the deists Voltaire and Adam Smith, for example—he was one of the most influential.