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What were they thinking?: The Impact of Mental State Explanations on Legal Decisions


People have an intuitive sense of what makes a good explanation for behavior. Confronted with a particular action, most people believe they could provide explanations that would be mitigating, that would be good explanations for the behavior. The law also has expectations about the impact of explanations. The American legal system explicitly classifies certain explanations as defenses that if believed should reduce punishment or excuse the behavior entirely. Across three studies, this dissertation finds that the reality of people’s behavior in response to an explanation often proves more complicated than laypeople or the law expect. Specifically, this dissertation considers the often unexpected ways that mental state explanations impact legal decisions.

Chapter 2 finds that ignorance of vital facts is not always a mitigating explanation. Across three experiments, we find that ignorance was a mitigating explanation for one class of crime, but not another, a cognitive distinction that mirrors a legal classification. This result runs counter to both intuitive expectation and scholarly argument that ignorance of the fact that makes an action illegal would always be a mitigating explanation. We also find statistical support for what may drive this distinction at a cognitive level, perhaps explaining how the crimes were classified by the legal system. We found that ignorance was a less mitigating explanation for crimes that appeared to have been set in an arbitrary manner, in that the line of illegality could have been drawn differently. Chapter 3 replicated the main findings of Chapter 2 in a non-legal setting, again finding that ignorance is a less mitigating explanation for some violations than others. In four experiments, we find that ignorance is a less mitigating explanation for violations of school rules that appear to have been set in an arbitrary manner. This study allowed us to manipulate arbitrariness experimentally, supporting our argument that it is an actor’s belief about the arbitrariness of the rule, not whether it has actually be set in an arbitrary manner, that determines whether mental state explanations will be mitigating. Chapter 4 approaches mental state explanations differently, asking how people evaluate these explanations and whether these evaluation strategies impact legal outcomes. We find that which mental state explanation a defendant offers does change how that explanation is evaluated, and that evaluation strategies do impact legal decisions. Thus, this dissertation proposes that the relationship between mental state explanations and legal outcomes is consequential but complicated.

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