The is-ought problem in ethics arises from the is-ought, fact-value distinction. It is the problem of moving from the factual to the normative, of obtaining a prescriptive claim from a set of descriptive claims.

The problem was first raised by David Hume in the 18th century; he pointed out that while many ethicists make claims about what ought to be solely from the basis of what is, there is a big difference between the two, and writers make an imperceptible switch from is claims to ought claims with no explanation offered. He argues that the move to the ought introduces a new relation or affirmation that needs to be clarified and justified. But he can find no justification, the implication being that such a move cannot ...