My text is a single and rather simple sentence from Rule 52(a) of the Federal Rules of Civil Procedure: Findings of fact, whether based on oral or documentary evidence, shall not be set aside unless clearly erroneous, and due regard shall be given to the opportunity of the trial court to judge of the credibility of the witnesses. My theme is equally simple.. Rule 52(a) serves a vital institutional role in allocating the responsibility and the power of decision between district courts and the courts of appeals. The "dearly erroneous" standard of appellate review established by the Rule is a fine example of the rule-making process working at its best. The Rule has been enormously successful. Professor Wright believes that no provision of the Civil Rules has been quoted and cited more often than this one.1 This success is due to the fact that the "clearly erroneous" phrase has no intrinsic meaning. It is elastic, capacious, malleable, and above all variable. Because it means nothing, it can mean anything and everything that it ought to mean. It cannot be defined, unless the definition might enumerate a nearly infinite number of shadings along the spectrum of working review standards. Learned Hand recognized early on that "[ilt is idle to try to define the meaning of the phrase .... ,,2 Much more recently, the Supreme Court has noted that "the meaning of the phrase 'dearly erroneous' is not immediately apparent. . .. "
Cooper, Edward H. "Civil Rule 52(a): Rationing and Rationalizing the Resources of Appellate Review." Notre Dame L. Rev. 63 (1988): 645-70.