Can Facts Alone Tell Us What We Ought to Do?

Once we know the facts, it is tempting to say, “therefore we ought to do this”. Yet that “therefore” usually contains a value premise that has not been stated.

In Book III of A Treatise of Human Nature, Hume notices that moral arguments often move from claims about what is the case to claims about what ought to be the case without explaining the new relation. A common twentieth-century reading turns this into the rule that a normative conclusion cannot be derived from purely factual premises. But it would also be a mistake to conclude that facts and values are unrelated. Facts can change what we know about consequences, capacities and conditions. They do not by themselves decide what deserves priority.

“This policy will reduce accidents” is an empirical claim. “We ought to give priority to reducing accidents” adds a value judgement. Only together can they support a practical conclusion.

The real value of the is–ought distinction, in my view, is not that it divides reality into two disconnected worlds. It forces an argument to expose its hidden value premises, so we can see whether the disagreement is about evidence or about what we are trying to achieve.

References
David Hume, A Treatise of Human Nature, Book III
https://davidhume.org/texts/t/3/full
Stanford Encyclopedia of Philosophy, Hume’s Moral Philosophy
https://plato.stanford.edu/entries/hume-moral/