The growth of American constitutional doctrine has been influenced, from the beginning, by the traditions of the Anglo-American COMMON LAW. Judges make constitutional law, as they make other kinds of law, partly on the basis of factual premises. Sometimes these premises are merely assumed, but sometimes they are developed with the aid of counsel. However they may be determined, the facts on which a court's lawmaking is premised are called "legislative facts." In modern usage they are sometimes contrasted with "adjudicative facts," the facts of the particular case before the court.
Not all constitutional questions concern the validity of legislation. In the 1970s and 1980s, for example, the Supreme Court went through a period of reappraisal of the EXCLUSIONARY RULE, which excludes from a criminal case some types of EVIDENCE obtained in violation of the Constitution. One factual issue repeatedly raised during this reconsideration was whether the rule actually served to deter police misconduct. In considering that question, the Court was not second-guessing the judgment of a legislature. Yet the question was properly regarded as one of legislative fact; its resolution would provide one of the premises for the Court's constitutional lawmaking.
More frequently, however, the courts consider issues of legislative fact in reviewing the constitutionality of legislation. In many cases, particularly when the laws under review are acts of Congress, the legislature itself has already given consideration to the same fact questions. Congress sometimes writes its own factual findings into the text of a law, explicitly declaring the actual basis for the legislation. In such cases the courts typically defer to the congressional versions of reality. Similar legislative findings are only infrequently written into the enactments of state and local legislative bodies, but even there the practice has recently increased. It seems unlikely, however, that judges, especially federal judges, will pay the same degree of deference to those legislative findings.
The courts' treatment of issues of legislative fact is thus seen as a function of the STANDARD OF REVIEW used to test a law's validity. When a court uses the most permissive form of the RATIONAL BASIS standard, it asks only whether the legislature could rationally conclude that the law under review was an appropriate means for achieving a legitimate legislative objective. The...