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 Massachusetts, the mental state of an individual plays a crucial role in determining their degree of guilt or culpability in criminal law. The mental states are typically ranked from most to least blameworthy as follows: (1) intentional, (2) knowing, (3) reckless, and (4) criminal negligence. Intentional actions are those done with the purpose of causing a particular result, while knowing actions are those where the individual is aware that their conduct is almost certain to cause that result. Reckless behavior involves consciously disregarding a substantial and unjustifiable risk, and criminal negligence refers to failing to perceive such a risk when an ordinary person would have. This failure must represent a significant departure from the standard of care expected in the situation. In Massachusetts, as in other states, the specific mental state required for a crime is defined in the relevant statutes, typically found in the Commonwealth's penal or criminal code. The prosecution must prove the defendant possessed the requisite mental state to secure a conviction for the offense charged.