Mistake of Law Defense

Mistake of Law is not a valid defense to a general intent crime. Even if the defendant’s mistake was reasonable, mistake of law is not a valid defense. (See People v. Marrero). The only exception is if a statute proscribing the defendant’s conduct has not been reasonably made available or if the defendant recently relied on a statute or judicial decision that was recently held unconstitutional.

However, under a specific intent crime, the defendant’s mistake of law is a valid defense whether reasonable or unreasonable. (See Cheek v. United States).

Compare to Mistake of Fact Defense

More Helpful Information: List of General Intent and Specific Intent Crimes

Mistake of Fact Defense

Under the Common Law, if the crime only requires general intent, the defendant’s mistake must be reasonable for mistake of fact to be a valid defense. If the crime is a specific intent crime, the defendant’s mistake can be reasonable or unreasonable. This reasonableness is first a legal conclusion, then it goes to the jury to determine whether or not the mistake was reasonable.

Under the MPC Section 2.04, the defendant’s mistake must go towards negating the mens rea required for the crime. If the crime only requires general intent, the mens rea is going to default to recklessness.

See Regina v. Prince for an example of mistake of fact.

Compare to Mistake of Law

Mens Rea

A defendant must have a “guilty mind” or mens rea in order to be found guilty of a crime. Under the Common Law, the mens rea or the “guilty mind” was divided into four categories and the defendant’s mens rea must fall into one of these categories or else he cannot be guilty of an offense:

1.   Intentional – the defendant must have intended the conduct and the result of his conduct

  • Note: Transferred intent – if the defendant intended to kill A, and B jumps in front of him, the defendant’s intent to kill A transfers in his trial for the murder of B

2.   Knowledge – the defendant knew that the result was reasonably likely (focusing on the effect/result)

3.   Reckless –  willful and wanton (based on a reasonable person)

4.   Negligence – defendant did not exercise a standard of care that a reasonable person would have exercised in similar circumstances

The four categories above can be divided amongst specific intent crimes and general intent crimes:

  • Specific intent usually includes intentional and knowledge based crimes. For a specific intent crime, the mens rea will typically be written into the statute (i.e. intentionally)
  • General intent usually includes reckless and negligence based crimes. All that is required is that the defendant intended the conduct as opposed to the conduct and result.

The Modern Penal Code (MPC ) Section 2.02 tried to distinguish between the gray areas between the four categories by further defining Purposely in 2.02(2)(a), Knowingly in 2.02(2)(b), Recklessly in 2.02(2)(c), and Negligently in 2.02(2)(d). Here is the result of the changes:

1.   Purposely – essentially grouped conduct and result; looked at conduct and result as an either/or instead of and

2.   Knowingly – “high probability;” the focus is now on the conduct as well as the result;

3.   Reckless – “substantial and unjustifiable risk;” a conscious disregard that the result will occur (defendant does not know about the result); looks at the offense from the defendant’s (subjective) and reasonable person point of view

4.   Negligence – “should be aware;” objective standard that looks for justifiability


More Helpful Notes: Specific Intent Crimes List

Mens rea, Actus reus, and Attendant Circumstances

Common law defined criminal conduct by first looking at the mens rea or the offender’s “guilty mind.” Second, the common law looked at the actus reus or the offender’s “guilty act.” Finally, the common law weighed in the attendant circumstances. An important skill for a law school student is to be able to locate the mens rea, actus reus, and attendant circumstances in a definition of a crime.

For example, common law battery was defined as:

“The offense of battery occurs when a person actually and intentionally touches or strikes another against his or her will.”

  1. To determine the mens rea look for what describes the offender’s state of mind. Here, it is “intentionally.”
  2. To determine the actus reus look for what describes the offender’s action(s) that makes him guilty. Here, it is “actually…touchers or strikes another.”
  3. To determine the attendant circumstances look for the factors stem from the point of view of someone other than the defendant and that aggravate or mitigate the amount of culpability. Here, it is “against his or her will.”

Here is the common law definition of battery with the mens rea, actus reus, and attendant circumstances highlighted:

“The offense of battery occurs when a person actually and intentionally touches or strikes another against his or her will.”

A quick note on attendant circumstances: When determining what are attendant circumstances, it does not matter if the actor knows or intends to touch against the victim’s will. The actor’s guilty mind is not a factor in determining the attendant circumstances. In fact, attendant circumstances is actually from the point of view of someone other than the defendant (typically the victim). Also, it may be helpful if you think of attendant circumstances as those factors that would be helpful in determining a sentence, factors than can aggravate or mitigate the crime such as the amount of culpability.

Law school students should also know that under common law, the mens rea only modified the actus, not the attendant circumstances. Under our modern view, the mens rea modifies everything in the definition.

Theories of Punishment – Utilitarian vs. Retribution Theorists

Much debate surrounds how to punish criminal offenders. Social norms, necessity, and social desirability are some of the factors that lawmakers balance when developing punishment statutes. Two different schools of thought, in regards to punishment, are discussed below:

Utilitarian Theorists

Premise: General punishment will deter the public from committing a crime

Utilitarian Theorists believe that punishment should be developed based on what is best for the public as a whole. A major focus is on the deterrent effect of a criminal statute because if a criminal statute deters a criminal act then the public benefits because the crime does not occur. Utilitarian theorists are “forward looking” as opposed to retribution theorists, discussed below.  The goal of utilitarian theorists is to prevent a crime from happening again. In a general sense this means that the punishment for a certain crime needs to be greater than the possible reward for committing the crime. A utilitarian theorist believes that if this appropriate level of punishment is met, most individuals will be deterred from committing the crime.

One of the problems with this approach is that it is often difficult to put the public on notice of the punishment of a particular crime. For example, most of the public is unaware of the exact punishment for petit larceny. Without notice this theory is practically thrown out the window because an individual cannot be deterred, in accordance with this theory, if he does not know the potential punishment. Another problem for utilitarian theorists is that, for the theory to work properly, other factors such as moral culpability or remorse cannot be weighed in determining punishment. If the public does not believe that punishment is consistent for every offense of a certain crime then, even with notice, the potential punishment may not deter an individual from committing a crime. Finally, even if punishment was consistent and the public had actual notice of the punishment for a crime, studies are conclusive on whether punishment is actually a deterrent to potential criminal offenders.

Premise: Specific punishment will reduce the rate of recidivism

Utilitarian Theorists believe that punishment should also be specifically tailored to the individual so that he will not commit future crimes. For example, an utilitarian theorist would believe strongly in incarcerating, or incapacitating, an individual who is likely to commit another crime (incapacitating could include the death penalty). If a criminal offender is in prison, he cannot commit another crime against the public. The practical problem with this belief is that it is hard to identify specific individuals who will become repeat offenders. In addition, this belief may be in conflict with the idea of punishing consistently. For example, if it is unlikely a criminal offender will repeat, than incarceration may not be the proper punishment. However, another criminal offender, who committed the same crime and the justice system believes is likely to repeat, may be incarcerated. The public may then believe that punishment is not consistent and therefore punishment will lose some of its deterrent effect. Finally, utilitarian theorists believe that rehabilitation of criminal offenders is good because they want to change the individual. However, studies are not conclusive that treatment programs really work.

Retribution Theorists

Premise: The punishment must fit the crime

Retribution Theorists are “backward looking” as opposed to the “forward looking” utilitarian theorists. Their beliefs could be summed up as “an eye for an eye.” A retribution theorists looks at the suffering of the victim to determine the level of punishment. The punishment of the criminal offender should be proportional to the suffering of the victim. This theory may also look at social norms when determining punishment. For example, a society may view the harm caused by cannabis to be less than the harm caused by cocaine so the punishment for an individual convicted of possession of marijuana may be less than the punishment for an individual convicted of possession of cocaine. One disagreement with this approach is that a retribution theorist does not care about future conduct of a criminal offender. Opponents of retribution theorists believe that this theory will not deter an individual from recidivism.