To select a verdict, jurors must integrate the evidence presented at trial with the law presented in the judge's instructions. Jurors are assumed to have no prior knowledge of the law or to set aside that knowledge after instruction. Several experiments (N = 489) tested these assumptions and revealed that (a) uninstructed Ss had built naive representations of crime categories that included legally incorrect information; (b) these representations contained category prototypes that influenced Ss' verdict choices; and (c) Ss' reliance on prototype information for verdict selection was resistant to change by instruction. Thus, Ss had prior knowledge of the law and did not set it aside after hearing the judge's instructions. This suggests that instructions must do more than create legal concepts where none exist; to be effective, instructions must revise jurors' existing concepts. A juror's task is to integrate the evidence presented at trial with the decision criteria defined by the law to select a legally appropriate verdict. Because most jurors have not had formal training in legal decision making (American Bar Association, 1968), the judge must instruct the jurors on the law at the time of trial. In a criminal trial, these instructions cover three types of law: (a) procedural law, including how to assess witness credibility and how to evaluate different kinds of evidence; (b) the requirements of proof, which explain that the defendant is innocent until the State proves beyond a reasonable doubt that the defendant is guilty; and (c) the substantive law, including definitions of the crimes charged (e.g., murder, robbery, and assault) and any defenses proposed (e.g., self-defense). For each crime, the law specifies a set of features that are singly necessary and jointly sufficient for guilt. Burglary, for example, requires that (a) the defendant knowingly entered a building, (b) the defendant did so without authority, and (c) the defendant did so with the intent to commit a crime (American Law Institute, 1962). Each of these criteria is a necessary condition for guilt; in other words, if any one of these conditions is not met beyond a reasonable doubt, then the juror is supposed to vote not guilty. These features are also jointly sufficient for guilt; if I would like to thank Sheri Springs-Phillips for her assistance with this research. She was an undergraduate honoris student in the Department of Psychology who collected most of the data for these studies and helped to write some of the crime situations used as stimuli. Her participation in this research is gratefully acknowledged. I would also like to thank Cathleen Milos.ChinazoOpia, and Scott Cho for collecting part of the data for Experiment 3.1 am grateful to Gene Borgida, Phoebe Ellsworth, Saul Kassin, Regina Schuller, and several reviewers for their extremely helpful comments on earlier versions of this article.

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of the individual user and is not to be disseminated broadly.1 Some states (e.g., Maryland and Indiana) instruct jurors that they have the right to nullify the law and vote not guilty if they believe a guilty verdict would be unjust under the circumstances (Hans & Vidmar, 1986). This instruction is a rare exception to the expectation that jurors will base their verdicts on the law as presented by the judge.

The authors are grateful to Robert Maura for his help in various phases of this research, and to R. Edward Geiselman for providing the crime clip used in Experiment 2. We would also like to thank Pamela Burke, Craig Smith, and Anthony Ahrens for their helpful comments on an earlier version of this article, and Andrew Blaine, Gary Rothschild, Kazu Sano, and Michael Tuchin for serving as confederates in these experiments.