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 between positive 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.