Is–ought problem
"In every system of morality, which I have hitherto met with, I have always remark'd, that the author proceeds for some time in the ordinary way of reasoning... when of a sudden I am surpriz'd to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not."
- David Hume, A Treatise of Human Nature (1739), Book III, Part I, Section I
Overview
The is–ought problem, also called Hume's guillotine or the fact–value gap, is the observation that no set of purely descriptive statements (about what is the case) entails a prescriptive conclusion (about what ought to be done) without the addition of at least one prescriptive premise. Facts alone do not tell you what to do.
Notes
- On my account of moral claims, the bridging premise is always a desire or interest. "Sugar causes ill health" (is) plus "we wish to avoid ill health" (want) yields "we ought not eat too much sugar" (ought). The want is the hidden premise in every moral claim, and once it is stated aloud the rest of the argument is empirical.
- The gap is not a problem for morality; it is a description of how morality works. It does mean that no amount of science will tell you what to value, which is why I disagree with Sam Harris's claim in The Moral Landscape that science can determine human values. Science can tell you what promotes well-being; it cannot tell you to want well-being, though almost everyone does.
- The Appeal to Nature is the most common way of trying to cross the gap illegitimately: "it is natural, therefore it is good".