Comprehension May not Occur: Issues of Modal Verb Ambiguity in Arizona and Utah State Jury Instructions

Jury instructions play a crucial role in the U.S. criminal justice system, yet the complexity of legal language can present comprehension challenges for jurors, who often lack extensive legal knowledge. Previous research within both legal and linguistic communities has highlighted the effectiveness of including linguistic features such as active sentences, reduced legal terminology, and increased use of modal verbs in improving jury instruction comprehension. The present study further investigates modal verb usage in jury instructions. The multiple possible interpretations of modal verbs could result in ambiguous meanings within jury instructions. Utilizing corpus linguistic analyses, the study examines civil jury instructions from Utah and Arizona. Frequency analysis of modal verbs in these instructions was carried out to establish general usage patterns of specific modal verbs within the two sets of jury instructions. Additionally, an investigation into instances of potential ambiguity was conducted using an adapted categorization of modal verb functions based on Biber et al.’s (1999) framework. Results indicate that among the nine primary modal verbs examined, instances of potential ambiguity are limited to the modal verbs may and can – specifically, the negated forms of these modal verbs. Additionally, a small follow-up comprehension survey shows that lay readers are most likely to diverge in their interpretations of may. Based on these findings, we propose recommendations for slight adjustments to Arizona and Utah jury instructions to enhance clarity in modal verb usage. Potential suggestions include replacing ambiguous modal verbs with less ambiguous modal verbs, incorporating clarifying adverbial phrases or clauses, and utilizing more degree adverbs and adjectives to aid juror comprehension.