Culpability (Blameworthiness) is the state of deserving to be blamed for a crime or offence.

Modern crimes codes in the United States usually make distinct four degrees of culpability.

Legal definitions are:

1. A person acts intentionally with respect to a material element of an offense when:
   1. if the element involves the nature of his conduct or a result thereof, it is his conscious object to engage in conduct of that nature or to cause such a result; and
   2. if the element involves the attendant circumstances, he is aware of the existence of such circumstances or he believes or hopes that they exist.
2. A person acts knowingly with respect to a material element of an offense when:
   1. if the element involves the nature of his conduct or the attendant circumstances, he is aware that his conduct is of that nature or that such circumstances exist; and
   2. if the element involves a result of his conduct, he is aware that it is practically certain that his conduct will cause such a result.
3. A person acts recklessly with respect to a material element of an offense when he consciously disregards a substantial and unjustifiable risk that the material element exists or will result from his conduct. The risk must be of such a nature and degree that, considering the nature and intent of the actor's conduct and the circumstances known to him, its disregard involves a gross deviation from the standard of conduct that a reasonable person would observe in the actor's situation.
4. A person acts negligently with respect to a material element of an offense when he should be aware of a substantial and unjustifiable risk that the material element exists or will result from his conduct. The risk must be of such a nature and degree that the actor's failure to perceive it, considering the nature and intent of his conduct and the circumstances known to him, involves a gross deviation from the standard of care that a reasonable person would observe in the actor's situation.

(The above has been quoted verbatim from the Pennsylvania Crimes Code (http://members.aol.com/StatutesPA/18.html). That in turn derives from the American Law Institute's Model Penal Code, which is the basis for large portions of the criminal codes in most states. The only difference is that the MPC uses "purposely" instead of "intentionally".)

In short:

• A person causes a result purposely/intentionally if the result is his/her goal in doing the action that causes it,
• A person causes a result knowingly if he/she knows that the result is virtually certain to occur from the action he/she undertakes,
• A person causes a result recklessly if he/she is aware of and disregards a substantial and unjustifiable risk of the result occurring from the action, and
• A person causes a result negligently if there is a substantial and unjustifiable risk he/she is unaware of but very much should be aware of.

The first two types of culpability are each a subset of the following. Thus if someone acts purposely, they also act knowingly. If someone acts knowingly, they also act recklessly.

The definitions of specific crimes refer to these degrees to establish the necessary mens rea (mental state) necessary for a person to be guilty of a crime. The stricter the culpability requirements, the harder it is for the prosecution to prove its case.

For instance, the definition of first degree murder (again in PA) is "A criminal homicide constitutes murder of the first degree when it is committed by an intentional killing." Thus to be guilty of murder in the first degree, one must have an explicit goal in one's mind to cause the death of another. On the other hand, reckless endangerment has a much broader requirement: "A person commits a misdemeanor of the second degree if he recklessly engages in conduct which places or may place another person in danger of death or serious bodily injury." Thus to be guilty of this one only needs to be aware of a substantial risk he is puting others in danger of; it does not have to be one's explicit goal to put people in risk. (But, if one's goal is to put others in substantial risk of death or serious bodily injury, this is, of course, sufficient.)

There is one more type of culpability, and that is strict liability. In strict liability crimes, the actor is responsible no matter what his mental state; if the result occurs, the actor is liable. An example is the felony murder rule: if one commits a qualifying felony (see the article) during which death results, one is held strictly liable for murder and the prosecution does not have to prove any of the normal culpability requirements for murder. (They still have to prove, of course, that the defendant committed the felony.)