 This skeptical/critical attitude underlies a significant tension in the age. While it is common to conceive of the Enlightenment as supplanting the authority of tradition and religious dogma with the authority of reason, in fact the Enlightenment is characterized by a crisis of authority regarding any belief. This is perhaps best illustrated with reference to David Hume’s skepticism, as developed in Book One of A Treatise of Human Nature (1739–40) and in his later Enquiries Concerning Human Understanding (1748). While one might take Hume’s skepticism to imply that he is an outlier with respect to the Enlightenment, it is more convincing to see Hume’s skepticism as a flowering of a crisis regarding authority in belief that is internal to the Enlightenment. Hume articulates a variety of skepticisms. His “skepticism with regard to the senses” is structured by the epistemological problem bound up with the way of ideas, described above. Hume also articulates skepticism with regard to reason in an argument that is anticipated by Bayle. Hume begins this argument by noting that, though rules or principles in demonstrative sciences are certain or infallible, given the fallibility of our faculties, our applications of such rules or principles in demonstrative inferences yield conclusions that cannot be regarded as certain or infallible. On reflection, our conviction in the conclusions of demonstrative reasoning must be qualified by an assessment of the likelihood that we made a mistake in our reasoning. Thus, Hume writes, “all knowledge degenerates into probability” (Treatise, I.iv.i). Hume argues further that, given this degeneration, for any judgment, our assessment of the likelihood that we made a mistake, and the corresponding diminution of certainty in the conclusion, is another judgment about which we ought make a further assessment, which leads to a further diminution of certainty in our original conclusion, leading “at last [to] a total extinction of belief and evidence”. Hume also famously questions the justification of inductive reasoning and causal reasoning. According to Hume’s argument, since in causal reasoning we take our past observations to serve as evidence for judgments regarding what will happen in relevantly similar circumstances in the future, causal reasoning depends on the assumption that the future course of nature will resemble the past; and there is no non-circular justification of this essential assumption. Hume concludes that we have no rational justification for our causal or inductive judgments. Hume’s skeptical arguments regarding causal reasoning are more radical than his skeptical questioning of reason as such, insofar as they call into question even experience itself as a ground for knowledge and implicitly challenge the credentials of Newtonian science itself, the very pride of the Enlightenment. The question implicitly raised by Hume’s powerful skeptical arguments is whether any epistemological authority at all can withstand critical scrutiny. The Enlightenment begins by unleashing skepticism in attacking limited, circumscribed targets, but once the skeptical genie is out of the bottle, it becomes difficult to maintain conviction in any authority. Thus, the despairing attitude that Hume famously expresses in the conclusion to Book One of the Treatise, as the consequence of his epistemological inquiry, while it clashes with the self-confident and optimistic attitude we associate with the Enlightenment, in fact reflects an essential possibility in a distinctive Enlightenment problematic regarding authority in belief.