Hume’s Guillotine
Behavioral New World
July 1, 2025
Hume’s Guillotine
Did that phrase catch your attention? It did mine. But as it turns out, I learned about this issue under a different name in my first economics class. Understanding it is vital for effective thinking.
David Hume was a Scottish economist and philosopher (as was Adam Smith; Scotland is punching above its weight here.) Hume is best known for his work, “A Treatise of Human Nature.” Although it focuses on psychology and morality, one could argue that he was an early behavioral economist.
In many introductory economics classes, including my first one as an undergraduate decades ago, one learns the difference between “positive” and “normative” economic statements. Positive economic statements are “is” statements, logical or factual. “If you raise the price of dolls, people will buy fewer of them” is a positive (logical) economic statement. “Positive” isn’t necessarily good: “The inflation rate is 50%” is also a positive (factual) economic statement.
Normative economic statements are “ought” or “should” statements. They reflect, either implicitly or explicitly, an underlying value or belief. (More on this in a moment.) Examples: “We ought to have a flat tax.” “We should pay teachers more.”
Hume argues that there is no inevitable connection between positive and normative statements, although positive statements can shed light on normative statements. His metaphorical guillotine severs the connection between is (positive) and ought (normative). Thus, Hume’s Guillotine is also referred to as “Hume’s is-ought problem.” Let’s explore this idea with some examples.
“We ought to have a flat tax” is based, consciously or not, on a value held by the person making the claim—it is a normative statement. Perhaps the claim is based on a notion of fairness such as “every dollar of income should be taxed at the same rate.” Alternatively, a tax scheme with higher rates for higher incomes might be considered fair because people with higher incomes can afford to pay taxes at a higher rate. Because these statements concern fairness, a value, they are normative/ought statements.
“A flat tax would increase GDP growth” is a positive/is statement. It can inform a normative decision if increased GDP growth is a desired goal. But Hume argues that the positive and normative are separate. As in the paragraph above, “fairness” does not lead inevitably to just one conclusion.
Although these examples are from economics, the is-ought problem is widely applicable. In their book, The Rise of Victimhood Culture, authors Bradley Campbell and Jason Manning state, “Sociology cannot tell us what the moral aims of a society should be, but it can help us in figuring out what social arrangements will achieve them.” (p. 189) “Moral aims” are normative. The “social arrangements” are positive, for example, “If we provide a universal basic income, the consequences will be…”
The is-ought problem is by no means limited to the social sciences. Consider: “Fusion nuclear produces cleaner energy than fission nuclear” is an “is” statement. “We should build more fusion reactors” is an “ought” statement.
The perceived validity of the “ought” statement depends on several factors, including the costs, both financial and environmental, of building and running fusion reactors. And what about knock-on effects, such as less coal mining? How much we are willing to pay, the importance we put on a clean environment, and how much we think less coal mining is a good thing—these are among the values that underlie the “ought” statement.
Let’s end on a positive statement, in both senses: If you distinguish between “is” statements and “ought” statements, you will make better decisions. Hume’s Guillotine, ironically, keeps your head on straight.