An Enquiry Concerning Human Understanding

David Hume published An Enquiry Concerning Human Understanding in 1748, three years after the better-known Treatise of Human Nature had, in his own description, “fallen dead-born from the press.” The Enquiry is a condensed and clarified version of the Treatise’s epistemological arguments, written for a broader audience. It succeeded: the Enquiry was widely read in Hume’s lifetime and established his reputation as the leading philosopher of the Scottish Enlightenment.

The book’s central project is an investigation of the limits of human knowledge. What can we actually know, and how? Hume’s answer, worked out across twelve sections, is deeply unsettling. We cannot rationally justify most of what we believe.

We believe in causation — that one event causes another — but Hume argues that we never observe causation directly. We observe one event following another and develop a habit of expectation. The idea of necessary connection between cause and effect is not derived from experience; it is projected onto experience by the mind. This is not a comfortable conclusion: it means that the foundations of scientific reasoning cannot be rationally justified. Science works, in Hume’s account, not because it corresponds to some discovered structure of reality but because constant conjunction in past experience produces reliable expectations for future experience.

Section X, “Of Miracles,” is the most famous and controversial part of the book. Hume’s argument is this: a miracle is a violation of a law of nature. Our evidence for laws of nature consists of uniform human experience. Our evidence for any particular miracle is a finite number of testimonies. The evidence against the miracle — the whole weight of uniform experience — will always outweigh the evidence for it. Therefore, it is always more rational to explain a reported miracle in some other way than to accept that a law of nature was actually violated.

This argument does not prove that miracles cannot happen. It proves that believing a miracle occurred on the basis of testimony is never the most rational response. It remains the standard philosophical treatment of the subject.

The Enquiry ends with a famous passage: burn any volume that contains neither abstract reasoning about quantity or number, nor experimental reasoning about matters of fact. “It can contain nothing but sophistry and illusion.” Hume intended it as a provocation. It has served as one.