Mental states that determine the degree of guilt or culpability in criminal law are generally classified from highest (most worthy of blame or punishment) to lowest as: (1) intentional; (2) knowing; (3) reckless; and (4) criminal negligence.

A person acts with criminal negligence, or is criminally negligent, with respect to circumstances surrounding his conduct or the result of his conduct when he ought to be aware of a substantial and unjustifiable risk that the circumstances exist or the result will occur. The risk must be of such a nature and degree that the failure to perceive it constitutes a gross deviation from the standard of care that an ordinary person would exercise under all of the circumstances, as viewed from the accused person’s standpoint at the time of the alleged criminal negligence.

Criminal offenses or crimes often specify the culpable mental state the prosecution is required to prove to convict a defendant of the offense. These culpable mental states are generally defined in the relevant state or federal statutes—usually in the penal or criminal code.

In Maine, as in many jurisdictions, the mental state of an individual at the time of committing a crime is crucial in determining their degree of guilt or culpability. The mental states are ranked from most to least blameworthy: (1) intentional, (2) knowing, (3) reckless, and (4) criminal negligence. Criminal negligence in Maine is defined as failing to be aware of a substantial and unjustifiable risk that a reasonable person would have recognized, and this failure is a gross deviation from the standard of care expected in the circumstances. Maine's criminal statutes specify the required mental state for each offense, and the prosecution must prove the defendant had such a mental state to secure a conviction. These definitions and requirements are typically found in the Maine Criminal Code and are consistent with principles of criminal law across various jurisdictions in the United States.