The findings showed that, with or without instructions, laypeople were not able to reliably make the distinction, fundamental to most criminal codes, between the various criminal mental states. The data demonstrated that subjects were able to distinguish only between the most culpable level (criminal intent) and the least culpable (criminal negligence), whether generating their own definitions or relying on formal legal definitions. The findings suggest that legal definitions should be reworded in language that laypeople can understand or eliminated altogether. The American justice system may be vulnerable to error particularly in criminal cases where jury instructions include lesser offenses which require the jurors to decide on a criminal defendant's particular mental state. 4 tables, 1 note, and 27 references (Author abstract modified)