http://nationalparalegal.edu/public_documents/courseware_asp_files/criminalLaw/basicElements/ModelPenalCodeMensRea.asp
1. Purpose
A person acts purposefully (intentionally) if he acts with the intent that his action causes a certain result. In other words, the defendant undertakes his action either intending for, or hoping that, a certain result will follow.
2. Knowledge
A person acts knowingly if he is aware that his conduct will result in certain consequences. In other words, a person acts knowingly if he is aware that it is practically certain that his conduct will cause a specific result.
3. Recklessness
A person acts recklessly if he is aware of a substantial risk that a certain result will occur as a result of his actions. The risk must be substantial enough that the action represents a gross deviation from what a reasonable law abiding person would do.
The difference between recklessness and knowledge is that where a person acts knowingly he acts with the certainty that a certain result will follow from his actions. However, where a person acts recklessly, the person does not know for sure that a specific result will follow. Rather, he only knows that there is a substantial risk that the result will follow.
4. Negligence
A person acts negligently if they should have been aware of a substantial and unjustifiable risk that a certain consequence would result from their actions. Although the level of risk is the same for both recklessness and negligence, the difference between the two is that with recklessness, the actor must be aware of the risk involved with her actions, whereas, for negligence, the actor is not aware of the risks but should have known what those risks were. In other words, where Wilma sets the bomb off to go at 8:30, knowing that there is a risk that someone might get killed, she has acted recklessly. However, if for some reason, she doesnt recognize that someone might get killed, she has acted negligently because a reasonable person would be aware that someone could get killed if they were to put a bomb on an airplane.