Defenses

• Defense of infancy

This is an aspect of the public policy of parens patriae. In the criminal law, each state will consider the nature of its own society and the available evidence of the age at which antisocial behavior begins to manifest itself. Some societies will have qualities of indulgence toward the young and inexperienced and will not wish them to be exposed to the criminal law system before all other avenues of response have been exhausted. Hence, some states have a policy of doli incapax and exclude liability for all acts and omissions that would otherwise have been criminal up to a specified age. Thereafter, there may be a rebuttable presumption against the use of criminal sanctions except in more serious cases. Other states leave discretion to prosecutors to argue or the judges to rule on whether the child understood that what was being done was wrong.

The status of minor may also excuse liability in the civil law for contract, tort and other legal situations during which liabilities would otherwise attach to the infant. Where there is only minimal understanding, transactions entered into will be void, i.e. the infant is excused. When understanding grows in line with age, the law switches from excuse to exculpation, and transactions may be voidable, i.e. the courts will judge, whether in the particular circumstances, it would be right to favor the interests of the child or the interests of the other party or parties involved in the transaction. Hence, it would not be appropriate to allow a child knowingly to deceive innocent retailers or service providers into supplying value, and then allow him or her to avoid liability to pay a reasonable sum of money for those goods or services. This is a balancing of political and commercial interests.

• Insanity defense, mental disorder defences and the M'Naghten Rules

If individuals are a danger to society and/or to themselves but not responsible through a lack of understanding, there is no point in punishment (whether in the criminal or non-criminal sense). Punishment is only justified morally if the person understands that what was done was wrong and accepts the judgment of society as part of the process of expiation and rehabilitation. Hence, as with parens patriae, the state accepts the person as being in need of care, and offers or requires medical treatment instead of subjecting such people to the stress of having to undergo a trial as to liability.

• Settled insanity is defined as a permanent or "settled" condition caused by long-term substance abuse and differs from the temporary state of intoxication. In some United States jurisdictions "settled insanity" can be used as a basis for an insanity defense, even though voluntary intoxication can not, if the "settled insanity" negates one of the required elements of the crime such as mens rea.
• Automatism

This criminal defense straddles the divide between excuse and exculpation. It works by showing that the defendant's mind was not in control of the body's movements at the relevant time and that this loss of control was not foreseeable. For example, a diabetic suffering a hypoglycaemic attack will not be liable for any loss or damage caused. To that extent, it borrows from the policy excuse favoring those who are suffering from a mental illness, but allows the full trial as to liability to proceed. For a detailed comparative law discussion, see automatism (case law).

• Self-defense is, in general, some reasonable action taken in protection of self. An act taken in self-defense often is not a crime at all; no punishment will be imposed. To qualify, any defensive force must be proportionate to the threat. Use of a firearm in response to a non-lethal threat is a typical example of disproportionate force; however, such decisions are dependent on the situation and the applicable law, and thus the example situation can in some circumstances be defensible, generally because of a codified presumption intended to prevent the unjust negation of this defense by the trier of fact.

Exculpations

• Duress in criminal law and in contract law

In this situation, the defendant has actually done everything to break the law and intended to do it to avoid some threatened or actual harm. Thus, some degree of liability already attaches to the defendant for what was done. In law, the usual rule is that the defendant's motive for breaking the law is irrelevant although, in the criminal law, this may reduce the sentence. The basis of the defense argues that the threats made by the other person make the defendant's entire behavior involuntary and therefore the liability should be reduced or removed. The extent to which this defense should be allowed, if at all, is a simple matter of public policy. A state may say that no threat should force a person deliberately to break the law, particularly if this breach will cause loss or damage to a third person. Alternatively, a state may take the view that even though people may have ordinary levels of courage, they may nevertheless be coerced into agreeing to break the law and this human weakness should have some recognition in the law. For example, suppose that a group of terrorists kidnap A's family and instruct A to carry a large bomb into a crowded area as the price for the release of their family. If A carries out these instructions, making no effort to contact the police or to warn those in the danger area, the issue of liability for death and injury resulting depends on the state's values. This is a legal as well as a political decision. In the civil law, duress is similarly only an exculpation, rendering contracts and other transactions voidable, and offering only minor mitigation in the calculation of the amount of any damages payable.

• Mistake of fact in criminal law and in mistake in contract law

The fundamental policy operating here is ignorantia juris non excusat, i.e. the state cannot allow ignorance of the law to be a defense. This would unduly encourage the lazy and the deceitful to trade on their ignorance (real or otherwise). Thus, only mistakes relating to the factual basis of what is being attempted can form this defense and, in the majority of situations, it will only offer limited benefit to a defendant of ordinary capacity since the state owes no general duty to save citizens from the effects of their own ignorance or stupidity. Nevertheless, there may be limited circumstances in which people may honestly believe things that either prevent them from forming the requisite mens rea or from reaching an ad idem agreement.

• Provocation

This is an example of a purely mitigatory defense in that, in the few situations when it is allowed to operate, it only reduces the level of criminal liability. In most legal systems, it cannot extinguish liability. It is a natural part of human nature that people get angry when they are provoked. But the state has a positive interest in maintaining good order and therefore, no matter what is done or said, people are not supposed to react violently or to cause loss or damage. Even though certain forms of physical contact or particular words might cause even reasonable people to become seriously annoyed, the state cannot sanction or justify retaliation. Thus, in most aspects of the law, any loss of control is taken to be an aggravating factor that, in the criminal law or the law of intentional torts, might well lead to an increase in sentencing, or the award of punitive or exemplary damages.