A primary theme that runs throughout The Reasonableness of Christianity is John Locke’s belief that men who attempt to understand natural law and morality through their faculty of reason alone often fail at their task. But why is it that reason alone, also according to Locke, can explain Revelation?

The question this essay poses might seem somewhat straightforward: What is meant by the term “reasonable” when Locke described Christianity by this term in his 1695 work, The Reasonableness of Christianity? The answer might even seem intuitive: It means that our faculty of reason allows for an accurate interpretation and understanding of the Word. Indeed, Locke wrote that man can understand Revelation by his reason and thereby affirm Christianity as true. But the flaw and controversy of this argument was correctly noted by Locke’s critics when it was deemed not only illogical, but also tinging on heresy. The reasoning for this claim is as follows: If reason is the gatekeeper and ultimate arbiter of truth, then it would mean that it is reason, not Christianity, which has the last word in determining what is true or not. Put brusquely, reason—and not faith itself—is what validates faith. A closer exploration of the several arguments that Locke used in The Reasonableness of Christianity and in his Vindications of the Reasonableness of Christianity would mend this erred interpretation of Locke’s use of the word “reasonable” and reveal that the term is actually a compound definition that encompasses several elements of the relationship between reason and faith.

An initial reception of The Reasonableness purported that Locke was placing reason over revelation, stamping a mark of Socinianism on the book because Socinians were known for practicing a form of biblical theology that relied on reason over tradition to interpret revelation.[1] Still, this criticism of the famed political philosopher was not true. Locke might have arrived at similar conclusions to Socinians because he used an epistemological method that set aside traditions and instead applied an empirical method to determine the sense and authority of Scripture, but he was inclined to this approach due to his reasoning as an empiricist, not a Socinian.[2] Unlike Socinians, Locke is quite clear about his view that the faculty of reason is flawed.[3] While Locke would agree that Christianity is a self-evident truth that man can better understand through reason, he salvaged his argument from its impending theological pitfalls by adding that man needs Christianity to supplement his reason. In so doing, Locke eschewed accusations of Deism and responded to a common controversy in the 1690s that discussed the dissenting positions towards Scripture coming from Nonconformists, also known by their derogatory label as Arminians.[4]

Much of The Reasonableness demonstrates Locke writing as a thinker who was familiar with the other theological arguments of his time on the topic of reason and faith. By 1675, “reason” entered analytical and exegetical debates in theology as an attempt to redeem religion from a characterization of zeal and fanaticism.[5] Likewise, reason was also an intellectual weapon against religious nonconformists (Arminians) who preferred a plain interpretation of the Bible and against Anglicans whose theology eventually turned “into Socinian metaphor.”[6] By 1667, Latitudinarian, Arminian, and Socinian schools of thought were pervasive enough that Locke absorbed their arguments to enrich his own, though he never explicitly endorsed them.[7] Locke answered these schools, upholding that Christianity improves our lives by shaping our reason in order to be able to accept truths that are beyond our understanding and by helping us live a properly happy life through the moral conduct that Christianity inculcates.[8]

In The Reasonableness, Locke asserted that natural law is an authority to which everyone is universally obliged.[9] This concept of a natural law that dictated the ways in which man ought to comport himself in society was integral to his argument, and it was an argument that was influenced by the Latitudinarian perception of revelation because they regarded revelation as the reaffirmation of the mandates of natural law.[10] Locke was not a full Latitudinarian, however, but their strong influence over him merits further explanation on their views to explain why they were so unavoidable for this topic of faith and reason. Latitudinarians “reasoned themselves into an approbation” of the principles of Christianity although they never discredited the original truth that lay in Scripture.[11] Latitudinarians viewed reason as the vital component for the support of religion, which meant that natural law’s precepts were not restricted only to those men who knew Revelation; they could be understood and accessed by “unaided reason” as well.[12] Revelation, nonetheless, was still a necessary supplement to reason because it served as further evidence for people to obey natural law by way of religious mandate. And so, the definition of reason for a Latitudinarian, contained a contradiction that was noticed by theologians of the time: Reason was both the divine moral law as well as the means through which men could interpret it.[13] Similar to the problem with Socinianism, the Latitudinarian argument between reason and Revelation implied that reason was not a means to morality, but an active moral force in itself that rendered religion second-best as a moral agent in our lives—perhaps even as a discardable agent for those who believed they possessed a strong enough faculty of reason.

An initial point to emphasize about Locke’s dissent from other schools of thought is that he did not see reason as an entity that possessed moral judgement; such a characterization would elevate reason above Scripture. Instead, Locke wanted to prove that Christianity is accessible to all through Scripture, which is interpreted through our reason.[14] To do so, Locke used reason as a faculty of judgement that allowed men to understand Christianity as it is presented in Scripture. In A Second Vindication to the Reasonableness of Christianity, Locke asserted that man possesses “a distinct catalogue of fundaments, each whereof it is necessary for him explicitly to believe…whereof he should disbelieve, or deny any one…”[15] This statement reveals the first component of Locke’s “reasonableness” of Christianity: Reason is an intrinsic faculty of judgement and knowledge that permits us to understand Christianity. This component requires corroboration by way of Locke’s other writings: When he was writing about the truths of Revelation in An Essay Concerning Human Understanding, Locke also described reason as a method for judgement. In Chapter 18 of Book IV he wrote that “it still belongs to reason to judge of the truth of [Scripture] being a revelation, and of the significance of the words wherein it is delivered.”[16]

But Locke’s understanding of why Christianity is “reasonable” does not stop at exegetical interpretation. Locke also considered reason to be the vital agent that reconciled the two sources of moral authority in the lives of men: Natural law and revelation.[17] In The Reasonableness, Locke expressed a problem: Reason as an intrinsic faculty of judgement is flawed. A primary theme that runs throughout The Reasonableness is his belief that men who attempt to understand natural law and morality through their faculty of reason alone often fail at their task. Locke writes,

But Natural Religion in its full extent, was nowhere, that I know, taken care of by the force of Natural Reason… ’tis too hard a task for unassisted Reason, to establish Morality in all its parts upon its true foundations; with a clear and convincing light… Experience shews that the knowledge of Morality, by meer natural light, (how agreeable soever it be to it) makes but slow progress, and little advance in the World. And the reason of it is not hard to be found in Men’s Necessities, Passions, Vices, and mistaken Interests.; which turn their thoughts another way… ’tis plain in fact, that humane reason unassisted, failed Men in its great and Proper business of Morality. It never from unquestionable Principles, by clear deductions, made out an entire Body of the Law of Nature. And he that collect all the Moral Rules of the Philosophers, and compare them with those contained in the New Testament, will find them to come short of the Morality delivered by our Saviour…[18]

Locke expands on the problems with unassisted reason and natural religion by taking the “unassisted” moral writings of philosophers like Epicurus, Seneca, Zeno, Confucius, and others as an example. During the time when they were writing, Locke explains, the law of nature was manipulated and corrupted into whatever was “convenient;” because of this lack of intellectual integrity, Locke asserts that philosophers would never be able to establish a universal concept of morality that would rally mankind together.[19] Reason, so far, is established as a faculty of judgement that is susceptible to error that Christianity helps to avoid. But if Locke says that man cannot know natural law by reason alone, then why is it that reason alone can explain Revelation? Since this question isn’t answered explicitly by Locke, we can infer that reason is missing something. On the other hand, by virtue of its noble action that seeks to understand established truth, reason is also aided by something. That something is Christianity, which according to Locke can and ought to supplement our reason in order for it to be fully formed. Reason is not a singular, homogenous, and intransigent faculty of judgement. This response, then, reveals another facet of why Christianity is reasonable: Christianity perfects our reason by working with it and enhancing it.

Locke explained in the above excerpt that Christianity aids man’s reason in the business of morality. As concerns morality, Locke establishes that whatever is “universally useful” as the standard to which men ought to “conform their manners” needs to be validated from “the authority of either reason or Revelation.”[20] If this is the case, then the effectiveness by which morality is inculcated is also a factor that Locke takes into account when considering what constitutes reasonableness. Thus, Christianity, as it is revealed in Revelation, is superior to man’s limited reason, and a man whose reason has yet to be aided by the light of Christianity would be wise to heed to the authority of Revelation for the sake of his moral formation. He wrote, “The view of Heaven and Hell, will cast a light upon the short pleasures and pains of this present state; and give attractions and encouragements to Virtue, which reason, and interest, and the Care of our selves, cannot but allow and prefer. Upon this foundation, and upon this only, Morality stands firm, and may deny all competition.”[21]

From the dichotomy that Locke drew between natural law and Revelation, and from his preference of Revelation over natural law as the better alternative because it supplies man’s reason with a necessary element or morality, we can infer a third component of Locke’s understanding of what “reasonableness” means: Christianity is useful to inculcate morality. This element is a practical point that Locke makes because he explains that Revelation helps to direct men to be more moral, which leads them to live as better citizens. In the excerpt above Locke is mentioning how morality is the “great business” of reason, but also how reason fails at this task because it alone has been insufficient to inculcate a full sense of morality. It is in this gap that religion can insert itself as that missing link between reason and morality, making it “reasonable” to use Christianity.

Locke’s definition of reasonableness is far more nuanced than it might have initially appeared. To recapitulate, Christianity is reasonable 1) because we understand it through an intrinsic faculty of judgement and knowledge (reason) which all men possess; 2) because that faculty (reason) alone is flawed and has misdirected men towards error over the years so Christianity rectifies it; and 3) because Christianity’s positive effect is measurable by its usefulness in society. Interestingly, Locke understood the term “reasonableness” in several facets: One was derived from the literal root of the word—that is, from its relationship with reason itself; another was derived from an epistemological exploration of reason’s capabilities, finding it to come up short on its own; and another was a practical interpretation of “reasonableness” that was contingent on its use in society, which he calculated through an empirical analysis of Christianity’s better guarantees for proper social conduct through its inculcation of morality. Simplifying Locke’s argument, therefore, to Socinian thought that made Christianity’s reasonableness contingent on its agreeableness with reason misses the mark altogether. Locke’s concept of reason, and what he means by “reasonableness” is most succinctly paraphrased in the following analogy and image that he painted for his readers:

He that Travels the Roads now, applauds his own strength and legs, that have carried him so far in such a scantling of time; And ascribes all to his own Vigor, little considering how much he owes to their pains, who cleared the Woods, drained the Bogs, built the Bridges, and made the Ways passable, without which he might have toiled much with little progress.[22]

To summarize the analogy above, reason is a morphing mindset that develops with experience; it allows man to understand and analyze the world through his own cognition, but it is also susceptible to a pride in judgement that would blind man from realizing that the very truths he is trying to decipher have already been elucidated by Christianity.

We might characterize him as a radical empiricist opposed to zealous Christians, but Locke’s conception of reason and the role that reason plays in religion and revelation strikes as being much more centrist. In A Second Vindication of the Reasonableness of Christianity, Locke explained that the “chief” purpose for his writing The Reasonableness was to convert Deists and “weak Christians;” “those who are not fully satisfied with the reasonableness of [Christianity].”[23] In fact, Locke’s mission in The Reasonableness was not meant to be a comprehensive discussion of Christianity and all its theological tenants. Locke reminded his readers that he is defining the reasonableness of Christianity by an important clause in his title, “…as delivered in the Scriptures.” In other words, Locke is not analyzing Christianity under any philosophical or theological principles, just from what he can understand from Scripture; this fact hints at why Locke avoided addressing controversial theological issues regarding Christianity and reason (like the mystery of the Trinity, for example) in his work. Locke admitted that it is difficult to know how much authority to allocate to the interpretation of Scripture, the authority of the church, and the illumination by the Holy Spirit.[24] But instead of weighing in on these topics, Locke focused on tangible concepts made manifest in the lives of men to persuade them of the advantages of Christianity. There are indeed theological mysteries in Christianity that are in many respects above reason, but these were not Locke’s primary concern in The Reasonableness. His focus, instead, was on the benefits that come from the Christian faith, as the best guarantor for living a moral and fulfilling life.

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Cragg, Gerald R., Reason and Authority in the Eighteenth Century (Cambridge, 2013).

Locke, John, and Alexander Campbell Fraser (ed.), An Essay Concerning Human Understanding (London, 1894).

Locke, John, and Higgins-Biddle, John C. (ed.), The Reasonableness of Christianity as Delivered in the Scriptures (Oxford, 2007).

Locke, John, and Nuovo, Victor (ed.), Vindications of the Reasonableness of Christianity (Oxford, 2016).

Marshall, John, John Locke: Resistance, Religion and Responsibility (Cambridge, 1996).

Nuovo, Victor, John Locke and Christianity: Contemporary Responses to the Reasonableness of Christianity (Bristol, 1997).

Rivers, Isabel, Reason, Grace and Sentiment: A Study of the Language of Religion and Ethics in England, 1660-1780: Whichcote to Wesley (Cambridge, 2005).

Sorkin, David Jan, The Religious Enlightenment: Protestants, Jews, and Catholics from London to Vienna (Princeton, 2011).

1 John Locke and Victor Nuovo (ed.), Vindications of the Reasonableness of Christianity (Oxford, 2016), pp. xi-xiii.

2 Locke, Vindications, p. xiii.

3 John Locke, and John C. Higgins-Biddle (ed.), The Reasonableness of Christianity as Delivered in the Scriptures (Oxford, 2007), pp. 149-151.

4 Locke, The Reasonableness, p. xvii.

5 John Marshall, John Locke: Resistance, Religion and Responsibility (Cambridge, 1996), p. 126.

6 Ibid.

7 Ibid., p. 119.

8 Locke, The Reasonableness, pp. 162-163.

9 Ibid. p. xcvi.

10 Ibid., 122.

11 Isabel Rivers, Reason, Grace and Sentiment: A Study of the Language of Religion and Ethics in England, 1660-1780: Whichcote to Wesley (Cambridge, 2005), p. 65.

12 Ibid.

13 Rivers, Reason, Grace and Sentiment, p. 65.

14 Locke, The Reasonableness, p. xix.

15 Locke, Vindications of the Reasonableness of Christianity, p. 74.

16 John Locke, An Essay Concerning Human Understanding, (London, 1894) p. 424.

17 Locke, The Reasonableness, p. 148.

18 Ibid. p. 149.

19 Ibid. pp. 151-152.

20 Ibid., pp. 151-152.

21 Ibid., 163.

22 Ibid. p. 156.

23 Locke, A Second Vindication, p. 100-101. pp. 149-151 in the original.

24 John Marshall, John Locke: Resistance, Religion and Responsibility (Cambridge, 1996), p. 23.

The featured image is “Portrait of John Locke” (1697) by Godfrey Kneller (1646-1723), and is in the public domain, courtesy of Wikimedia Commons. It has been brightened for clarity.

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