By Elena Yi-Jia Zeng

Richard Tuck argues in Philosophy and Government that “a truly modern and ‘scientific’” approach to ethics and politics was inaugurated in the seventeenth century as a response to scepticism. We are also told in the concluding remark that the story extended well into the eighteenth century. Yet, the much-anticipated sequel never arrives, which leaves us wondering what, as Tuck called it, “the various transformations” in the period “between Hobbes and the early eighteenth century” could be (xv, 348). A decade after the publication of Philosophy and Government, Richard Popkin finished the third edition of The History of Scepticism, expanding his narrative in the first two editions to cover the late seventeenth century. Coincidentally, both Tuck’s and Popkin’s stories close on the brink of the High Enlightenment, where David Hume began to challenge the foundation of all human knowledge while at the same time advancing the Enlightenment project of constructing the “science of man.” How could Hume carry out these seemingly paradoxical lines of inquiry at the same time? The “transformations” Tuck alluded to were the missing piece of the puzzle.

It was an epistemic question that underlay the transformations, which manifest themselves in the attempts to shift intellectual authorities from the Church to the individuals, and from the Aristotelian worldview to scientific knowledge claims. These challenges marked the return of scepticism after the wars of religion and the rise of the “Pyrrhonian crisis” in the early modern period (xix). While the former challenged the grounds of Christianity in the quarrels between Protestants and Catholics, the latter arose from the revival of ancient scepticism owing to the French translation of Sextus Empiricus’ works. Philosophical scepticism, as a result, was employed in religious debates, given its usefulness for “the criterion problem’ (5–16, 509). The criterion problem for early modern thinkers at the time was the quest to find the standards of legitimising religious truth, while its origin in ancient Greece was the Pyrrhonists” quest for the principles of (mostly philosophical) judgment. It urged many philosophers, including Michel de Montaigne, Pierre Charron, Pierre Gassendi, François de la Mothe le Vayer and Pierre Bayle, to raise doubts on the possibility of justifying religious belief as well as social norms via some solid criterion.

Scepticism at the time encouraged the attempt to subvert Aristotelian metaphysics and the recognition of the human mind’s limits. Descartes adopted methodological doubts to search for a certain ground for his science and thus claimed that scepticism was something to be overcome. The Cartesians, most notably Nicolas Malebranche, identified the weakness of the mind by means of the sceptical mode of thinking. But the purpose of doubt was not to embrace scepticism; instead, scepticism was a means to tackle human fallibilities caused by the imagination and the senses. Learning the correct ways to doubt, in Malebranche’s view, would help us to discover the truths (187–88).

However, Descartes and Malebranche were soon attacked by Pierre-Daniel Huet, whose aim was to use scepticism to resist the rationalist philosophy of his time. For Huet, Cartesian reason was the speculation that could not be the foundation of knowledge since reason itself was a limited and fallible faculty (94–99). He argued for a sceptical position that one could only attain truths by investigating empirical evidence rather than seeking certainty from the cogito—the Latin word for “I think”—which was a subjectivist foundation of philosophising for the Cartesians (xxix). Bayle carried on the subjects of scepticism regarding religion and human understanding (xviii–xli, xxxv, 13), but what distinguished him from his predecessors was his open defence of scepticism. That is, scepticism for him was no longer a position that needs to be overcome or an instrument that should only be employed to seek epistemological certainty. His positive view on scepticism also enabled him to advance several arguments which subsequently became essential for Hume. First, he contended that belief or disbelief in Christianity was irrelevant to morality (399–408). Second, popular opinion could not be the foundation of belief or philosophical controversies (Ch. 10 and 12). Third, superstitious beliefs could easily arise from common life, which gave priests and politicians the chances to manipulate people (§179). As we can see, the French revival of scepticism became a persistent polemic on the role of scepticism in science and philosophy as it went into the early eighteenth century. At the heart of the debates between the sceptics and the anti-sceptics was the concern over the limits of human understanding (18), a topic that continued to preoccupy eighteenth-century British thinkers.

How scepticism progressed in the Enlightenment period remains controversial. The narrative advanced by Popkin is that the Huet–Bayle tradition did not thrive in France but rather in Britain—specifically in the hand of Hume alone. Although the French philosophes generally admired Bayle’s works, their confidence in the progress of reason prevented them from pursuing sceptical philosophy (1–16). Yet, the trajectory of the sceptical tradition was not as straightforward as it was conventionally thought by Popkin. There were a variety of debates over scepticism preceding Hume, which means, as I would argue, that Hume’s connections to the Huet–Bayle tradition were not a linear relationship. In Britain, the most noteworthy development in this period was that scepticism about the limits of human understanding encouraged the progress of scientific knowledge. Members of the Royal Society—such as Robert Boyle, who even published a book entitled The Sceptical Chymist—consciously employed what they considered as Pyrrhonian scepticism to challenge Aristotelian science. For them, scepticism was a technique for detecting errors and examining the validity of their predecessors’ findings. The scientists’ aim was to unveil the hidden causes of natural phenomena, which, in their view, amounted to the proof of God’s authorship to the natural world. Hence natural science and natural theology were closely connected, given the scientists’ belief that the limits of human understanding could be overcome by attributing the unintelligible aspects of causality to God’s omnipotence. This development marked a shift in the strategy of justifying belief as well as the criteria of certainty.

John Locke’s position in relation to this development was rather complicated. His theory of ideas argued that experience was the only ground for knowledge, but he also attempted to prove that religious belief could achieve the same degree of certainty without the support of empirical evidence. In the debates over moral certainty, Locke, on the one hand, considered the beliefs derived from probable judgment as “Faith, or Opinion” rather than knowledge in the strict sense; but, on the other hand, we could not exclude them from scientific research since probable judgment was what we have for the knowledge of the external world (IV. II. 14–15). Locke was sceptical about science’s capacity of discovering the “real essence” of substance, as there is always something we “know not what” behind the appearance of external objects (Ibid., II. XXIII. 2; III. III. 15). Yet, he was at pains to prove that the knowledge of the existence of God was demonstrable—it was intuitively certain even though its nature was unknown to us (Ibid., IV. X). Locke’s differentiation among faith, opinion and knowledge gave reason a crucial role in evaluating epistemic certainty, which was the ground for religious justification. According to him, one would appeal to faith when there was no rational justification for divine revelation (Ibid., IV. XII. 2–3). But reason remains crucial to judge the “certainty or probability” of a revelation (Ibid., IV. XVIII. 2 and 8), otherwise religion would become “extravagant Opinions and Ceremonies” and give rise to enthusiasm (Ibid., IV. XVIII. 11, IV. XIX. 2–4).

Differentiating faith and opinion from knowledge was Locke’s attempt to explain the possibility of the latter, which served as his response to the sceptical challenge regarding human understanding. His ultimate goal was to accommodate religious belief with his theory of ideas. Ironically, Hume, largely inspired by Locke’s theory, was able to develop a set of arguments that put philosophy against superstitious belief. Religion, among other forms of superstition, was not justifiable since its explanation appealed to an incomprehensible cause that exceeded the limits of human understanding. It was a groundless system of belief that could hardly establish any degree of certainty.

Hume’s antithesis between philosophical and superstitious belief signifies that his scepticism operates in the confrontation between philosophy and theology (12.1–2). Not only does it show Locke’s aim of reconciling the two has failed in Hume’s eyes, but it also exposes the fact that many of our beliefs are not rationally justifiable ( Specifically, Hume’s scepticism about the senses indicates further that unjustifiable belief originates in the fallibility of our faculties where they misattribute the same identity to a discontinuous object. Misattribution produces the fiction that constitutes false belief. For Hume, superstitious beliefs often arise from “abstract reasoning”, that is, the inference produced by non-empirical judgment. It can be speculations from “false philosophy” or convictions in religion (, cf. But religious superstition is particularly dangerous for the wellbeing of mankind as it has led to warfare and monkish virtues ( Locke’s theory of ideas was a useful ground for Hume to identify these problematic beliefs. Like Locke, he found many ideas, such as substance or God, have no corresponding impressions and hence cannot be meaningfully understood. Yet, what made Hume a sceptic was his reluctance to admit the possibility of knowledge. That is, he took the unintelligibility of the nature of things as the primary obstacle for us to obtain truths. Our knowledge claims to the external world are contingent beliefs whose certainty is subject to the probability of evidence.

No one in the Age of Enlightenment would come forward to claim that his or her philosophy “is very sceptical” as Hume did (413). Yet, judging from the theological controversies and the debates related to scientific progress, there was a central theme—almost an anxiety—on epistemic certainty. Hume poked right on the sore point of this doubt. His predecessors prepared for him the intellectual climate that enabled him to re-orient the trajectory of the sceptical tradition. Pyrrhonian doubts, in Hume’s hands, no longer led to the crisis that annihilated all convictions, but a sophisticated mode of disagreement that gave rise to refined knowledge.

Elena Yi-Jia Zeng is a PhD Candidate in Political Thought and Intellectual History at King’s College, University of Cambridge. Her doctoral thesis “The Politics of Belief in Hume and Enlightenment Scepticism” looks into the nature and status of belief in Hume’s religion, morality and politics and his place in the sceptical tradition. She is also interested in modern British and Irish history.

Featured Image: John Brown, Gentleman on the Grand Tour (1773), image credit: National Trust.