Mens rea is the mental state of a criminal defendant. In Latin it means "guilty mind". Usually there are four levels of mens rea in crimes, in descending order of culpability:
The trend in trials and in legislation has been to weaken the requirement of proof of mens rea. A utilitarian view of justice does not depend on mens rea, while a moral view of justice does. Mens rea usually combined with actus reus is used to produce criminal liability. Very often the seriousness of an offence will vary depending on the level of mens rea. The most obvious example of this is in homicide where intent is generally required (with some limited exceptions) for murder, where as negligence is often sufficient for manslaughter.
William Blackstone famously observed, “in order to have a crime, there must be a vicious will.” However, in the modern regulatory state there are increasing attempts, particularly at the federal level, to create crimes that do not require proof of mens rea (often referred to as strict liability offences).
The difference between recklessness and negligence
A person is considered reckless if, in the circumstances, it is considered that they were aware of a risk of their behaviour, but proceeded anyway. Negligence however, accrues merely when you owe a duty of care to someone but through a mistake or inaction breach this duty. There is an actual knowledge component required with recklessness that is not present with negligence (or as it is commonly referred to in criminal law carelessness). An offence of reckless driving for example is much more serious than one of careless driving. In order to prove carelessness it is sufficient to prove a mistake, recklessness on the other hand requires an actual knowledge of the negative potential consequences of an action, but still taking that action.
- William Blackstone, Commentaries 21.