Culpability

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

Legal definitions of culpability, verbatim from the Pennsylvania Crimes Code, are:

1. A person acts purposely (criminally) 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.

In short:

• A person causes a result purposely 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 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 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.

例えば、ペンシルベニア州における第一級殺人罪の定義は、「故意の​​殺害によって行われた犯罪的殺人は、第一級殺人罪を構成する」です。したがって、第一級殺人罪で有罪となるには、他者を死に至らしめるという明確な意図がなければなりません。一方、無謀な危険行為には、はるかに広い要件があります。「他者を死亡または重傷の危険にさらす、またはさらす可能性のある行為に無謀に従事した者は、第二級軽犯罪を犯したことになる」。したがって、この罪で有罪となるには、他者を危険にさらす重大なリスクを認識しているだけでよく、人々を危険にさらすことが明確な意図である必要はありません。（ただし、他者を死亡または重傷の重大な危険にさらすことが意図であれば、もちろんそれで十分です。）

責任の形態にはもう一つ、厳格責任というものがあります。厳格責任犯罪では、行為者の精神状態に関係なく、行為者は責任を負います。結果が生じた場合、行為者は責任を問われます。例えば、重罪殺人の規則が挙げられます。検察が、ある人物が適格重罪（記事参照）を犯し、その結果として死に至ったことを合理的な疑いの余地なく証明した場合、その人物は殺人罪で厳格責任を負い、検察は殺人罪における通常の責任要件を証明する必要はありません。