What are the four mental states in the Model Penal Code?

In the context of criminal law, the Model Penal Code clarifies the concept of mens rea (the guilty mind) by establishing four distinct mental states:1

• Purposely: The actor acts with the conscious objective to engage in conduct or cause a specific result.1
• Knowingly: The actor is aware that their conduct is of a certain nature or that certain circumstances exist, and is practically certain that their conduct will cause a specific result.1
• Recklessly: The actor consciously disregards a substantial and unjustifiable risk that a material element of an offense will result from their conduct.1
• Negligently: The actor should be aware of a substantial and unjustifiable risk but fails to perceive it, representing a gross deviation from the standard of care that a reasonable person would observe.1

While most crimes require a showing of acting purposely, knowingly, or recklessly, negligent conduct only supports a criminal conviction if the specific definition of the crime includes it.1