Is–ought problem
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 descriptive 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.
For instance, a pair of scissors that cannot easily cut through paper can legitimately be called “bad” since it cannot fulfill its purpose effectively. Likewise, if a person is understood as having a particular purpose, then behaviour can be evaluated as good or bad in reference to that purpose. In plainer words, a person is acting “good” when that person fulfills that person’s purpose.