In U.S. constitutional law, rational basis review is the normal standard of review that courts apply when considering constitutional questions, including due process or equal protection questions under the Fifth Amendment or Fourteenth Amendment. Courts applying rational basis review seek to determine whether a law is "rationally related" to a "legitimate" government interest, whether real or hypothetical. The higher levels of scrutiny are intermediate scrutiny and strict scrutiny. Heightened scrutiny is applied where a suspect or quasi-suspect classification is involved, or a fundamental right is implicated. In U.S. Supreme Court jurisprudence, the nature of the interest at issue determines the level of scrutiny applied by appellate courts. When courts engage in rational basis review, only the most egregious enactments, those not rationally related to a legitimate government interest, are overturned. Rational basis review tests whether the government's actions are "rationally related" to a "legitimate" government interest. The Supreme Court has never set forth standards for determining what constitutes a legitimate government interest. Under rational basis review, it is "entirely irrelevant" what end the government is actually seeking and statutes can be based on "rational speculation unsupported by evidence or empirical data". Rather, if the court can merely hypothesize a "legitimate" interest served by the challenged action, it will withstand rational basis review. Judges following the Supreme Court's instructions understand themselves to be "obligated to seek out other conceivable reasons for validating" challenged laws if the government is unable to justify its own policies. History The concept of rational basis review can be traced to an influential 1893 article, "The Origin and Scope of American Constitutional Law", by Harvard law professor James Bradley Thayer. Thayer argued that statutes should be invalidated only if their unconstitutionality is "so clear that it is not open to rational question". Justice Oliver Wendell Holmes, Jr., a student of Thayer's, articulated a version of what would become rational basis review in his canonical dissent in Lochner v. New York, arguing that the word 'liberty', in the 14th Amendment, is perverted when it is held to prevent the natural outcome of a dominant opinion, unless it can be said that a rational and fair man necessarily would admit that the statute proposed would infringe fundamental principles as they have been understood by the traditions of our people and our law. However, the court's extensive application of economic substantive due process during the years following Lochner meant that