The is-ought problem, as articulated by Scottish philosopher and historian David Hume (1711–76), states that many writers make claims about what ought to be on the basis of statements about what is. Hume found that there seems to be a significant difference betweenpositive statements (about what is) and prescriptive or normative statements (about what ought to be), and that it is not obvious how one can coherently move from descriptive statements to prescriptive ones. The is–ought problem is also known as Hume’s law, or Hume’s guillotine.
A similar view is defended by G. E. Moore‘s open-question argument, intended to refute any identification of moral properties with naturalproperties. This so-called naturalistic fallacy stands in contrast to the views of ethical naturalists.