There are many ways that a person can seek to defend himself when he is charged with a crime. Some of those defenses are known as common law defenses because they arise not from a specific statute, but rather, from many years of law that has been passed down in society. Some of those defenses arise from similar legal doctrines, while others are very different in nature. This paper explores some of the common law defenses, their legal justifications, and some of their differences or similarities. It also discusses famous cases that have made use of these defenses in order to try to avoid criminal liability.

When a person is accused of committing a crime, there are certain defenses that he or she might raise in defense. Some of those defenses are things that the legislature of a state has decided to create specifically in order to give would-be offenders a way out. These are known as statutory defenses, as they arise and are given power because of the language of some statute. For instance, the Stand Your Ground laws in places like Florida are statutory defenses because they would not exist with the specific codification of the state legislature. Other defenses are known as common law defenses. These are defenses that arise not from some specific act of the legislature, but rather, from the common law traditions of a place. These are the supposed natural laws that people must abide by, and they are somewhat less specifically defined than statutory defenses. Common law defenses have many things in common and also dome critical differences, which will discussed and explored in this paper.

Lack of mental capacity is one of the top common law defenses. In many states, this is known as the insanity defense. This is a common law defense that admits that the person in question committed the act. Even while admitting that the person committed the act, it seeks to avoid criminal consequences of the basis of a person lacking the mens rea necessary for committing a crime. Under the American system of criminal law, a person has to do more than just act. He must also have the requisite criminal mindset to accompany the act. One who is insane does not have the mental capacity to formulate those criminal thoughts, and for that reason, the person must be considered innocent. John Wayne Gacy is perhaps one of the most famous people to have tried to use the insanity defense. The serial killer and rapist claimed that he should be acquitted because was not of sound mind while committing the crimes (Linedecker, 1993). In addition, Lorena Bobbitt, the woman who cut off her husband’s penis, attempted to avoid criminal consequences by claiming insanity (Dershowitz, 1994).

“Infancy” is a very similar common law defense. This defense notes that the person in question did commit the act, but that person should not be held responsible because he or she was under a certain age at the time. The idea behind this common law defense is that if people are of a certain age, they should not be held responsible for their actions. In essence, one must be of an age where he or she can understand right or wrong before society can assume that he or she had the so-called criminal mindset. These are similar defenses because they do not deny the act, but rather, seek to avoid consequences by way of a mitigating mindset factor.

Necessity is another common law defense. This defense claims that the person in question acted on the lesser of two evils. A good example of when this might be used would come if a person genuinely believed, and had reason to believe, that if he did not commit some act, then his family would be killed by another person. The basis for this common law defense is that a person’s decision-making is skewed by the presence of an exterior factor, making it so that his act was not the result of a criminal mindset. This, too, is similar to the previous two common law defenses in that it goes to the mindset of the offender rather than the actual act. It is different, however, because a person claiming necessity does not necessarily have to be insane or otherwise out of his mind. While the insanity defense depends upon the concept that a person is acting outside the bounds of how “normal” people think, the necessity defense is based upon the precept that the offender is doing precisely what any reasonable person would do under the circumstances.

Self-defense is perhaps the most commonly used common law defense. The law provides a person with a right to defend himself, or to defend another, against the threat of serious bodily injury. There is no requirement that a person allow himself to go through significant danger just to avoid injuring the person who is inflicting the danger. With that in mind, a person is allowed to use whatever force is necessary to avert the danger. In some cases, this might mean lethal force, given that the circumstances are of a kind that would demand that level of force. Self-defense is different from necessity in that it transforms the very nature of the act. While necessity is a legal doctrine that explains a criminal act, a self-defense claim transforms an illegal act into a justifiable one. While the legal distinctions are razor thin, they are important. A number of cases over time have included this particular defense. Recently, the George Zimmerman case in Florida, in which he shot and killed Trayvon Martin, was based upon a self-defense claim, with the man walking free because a jury found that he acted in self-defense (Blow, 2012).

Ultimately there are many common law defenses, and most of them arise from a central legal doctrine. Some, as mentioned above, do not seek to deny the criminality of the offense. Rather, they dispute, for one reason or another, the criminal mindset of the offender, which is required for there to be a crime at all. Others seek to change the nature of the act itself from criminal to non-criminal on the basis of external factors.