Famous David Hume Quotes Explained
David Hume was a Scottish philosopher, historian, and economist of the Scottish Enlightenment. Hume's <em>Treatise of Human Nature</em> (1739–40) and the <em>Enquiry concerning Human Understanding</em> (1748) define Anglophone scepticism. Below are eight of the most-quoted lines.
“Reason is, and ought only to be the slave of the passions.”
Part 3, Section 3
What it means
From the Treatise of Human Nature, Book II, Part 3. Hume's claim, deliberately provocative, is that reason on its own cannot motivate action; only the passions can. Reason serves the passions by identifying the means to ends the passions have already set, but it does not set the ends itself.
“Custom, then, is the great guide of human life.”
Variant (perhaps a paraphrase of this passage): It is not reason which is the guide of life, but custom.
What it means
From the Enquiry concerning Human Understanding, Section V. Hume's view is that inductive expectation — and so most of practical knowledge — rests on habit rather than rational demonstration. Custom does the work that pure reason cannot, and a creature lacking custom would be paralysed.
“A wise man proportions his belief to the evidence.”
Section X: Of Miracles; Part I. 87
What it means
From the Enquiry concerning Human Understanding, Section X, "Of Miracles." Hume's evidentialist principle: belief is a quantitative response to evidence, and extraordinary claims require correspondingly strong evidence. The maxim has been borrowed by twentieth-century sceptics and inherited as the "Sagan standard."
“Generally speaking, the errors in religion are dangerous; those in philosophy only ridiculous.”
Part 4, Section 7
What it means
From Hume's Essays, Moral, Political and Literary. Hume distinguishes the social consequences of intellectual error: a mistaken philosophical position embarrasses its holder, while a mistaken religious conviction can mobilise persecution. The asymmetry justifies special caution about religious confidence.
“All knowledge degenerates into probability.”
Part 4, Section 1
What it means
From the Treatise of Human Nature, Book I, Part 4. Hume's sceptical argument is that even deductive certainty becomes probabilistic when one accounts for the fallibility of the reasoner; the longer the chain, the more the probability of compounded error degrades the conclusion.
Attributed to David Hume:
“It is not contrary to reason to prefer the destruction of the whole world to the scratching of my finger.”
What it means
From the Treatise, Book II, Part 3, section 3. Hume's notorious example illustrates his point about reason and passion: reason can rank means but not ends, so no ranking of ends is irrational by reason alone. The line is often misread as an endorsement; it is a description of the limits of reason.
“When men are most sure and arrogant they are commonly most mistaken.”
§ 9.13 : Conclusion, Pt. 1
What it means
From the Enquiry and the Essays. Hume's epistemic principle is that confidence is inversely correlated with calibration: people who reach conclusions cautiously revise them readily, while people who reach conclusions decisively defend them long past the point at which they should have been revised.
“The corruption of the best things gives rise to the worst.”
Part X - With regard to courage or abasement
What it means
From the Essays, after a Latin proverb. Hume's claim is that genuine excellence is rare and accordingly fragile: when a society's best institutions degrade, the failure mode is more severe than for institutions that were never very good to begin with. The asymmetry has been borrowed by both conservatives and progressives.