by the parties. In other words, they will not reverse unless no one submitted any testimony, documentation, or other evidence which directly or indirectly (i.e., through reasonable inferences) supports a material fact, thereby implying that the finder of fact must have engaged in impermissible speculation with no reasonable basis in order to reach a verdict. If the parties presented conflicting evidence, appellate courts applying a "substantial evidence" standard assume that the jury or administrative agency resolved the conflict in favor of the prevailing party, and in turn, appellate courts must defer to such implicit findings about which side's witnesses or documents were more believable, even if they suspect they might have ruled differently if hearing the evidence themselves in the first instance. This is a highly deferential standard. Clearly erroneous Under the "clearly erroneous" standard, where a trial court (as opposed to a jury or administrative agency) makes a finding of fact, such as in a bench trial, that finding will not be disturbed unless the appellate court is left with a "definite and firm conviction that a mistake has been committed" by that court. For example, if a court finds, based on the testimony of a single eyewitness, that a defendant broke a window by throwing a 30-pound rock over 100 feet, the appeals court might reverse that factual finding based on uncontradicted expert testimony (also presented to the lower court) stating that such a feat is impossible for most people. In such a case, the appeals court might find that, although there was evidence to support the lower court's finding, the evidence taken as a whole—including the eyewitness and the expert testimony—leaves the appellate court with a definite and firm conviction that a mistake was committed by the Court below. Questions of law De novo Under de novo review, the appellate court acts as if it were considering the question for the first time, affording no deference to the decisions below. Legal decisions of a lower court on questions of law are reviewed using this standard. This is sometimes also called plenary review or the "legal error" standard. It allows the appeals court to substitute its own judgment about whether the lower court correctly applied the law. For example, as noted in Bose Corp. v. Consumers Union of United States, Inc., de novo review is required in the United States when First Amendment issues are raised on appeal.