Effects of necessary, sufficient, and indirect causation on judgments of criminal liability.

When has one essentially committed a crime? When are one's actions necessary for its occurrence or sufficient to bring it about under normal circumstances? Participants assigned punishments to 17 scenarios that varied as to the necessity and sufficiency of a perpetrator's actions in bringing about a murder; in some instances abnormal circumstances prevented the crime from coming about. The perpetrator's perceived contribution to the outcome was the strongest predictor of assigned liability, but perceived necessity and sufficiency were also predictors. All three measures mediated assignments of liability when relevant to a given case. In contrast to the stance taken in the Model Penal Code, liability assignments for sufficient cause scenarios were higher than those assigned to attempt scenarios, revealing that people regard actions that are ordinarily sufficient to bring about murder as requiring more punishment than less complete attempts.