In jurisprudence, an excuse or justification is a form of immunity that must be distinguished from an exculpation. In this context, "to excuse" means to grant or obtain an exemption for a group of persons sharing a common characteristic from a potential liability. "To justify" as in justifiable homicide means to "vindicate" or show the justice in the particular conduct. Thus, society approves of the purpose or motives underpinning some actions or the consequences flowing from them (see Robinson), and distinguishes those where the behavior cannot be approved but some excuse may be found in the characteristics of the defendant, e.g. that the accused was a serving police officer or suffering from a mental illness. Thus, a justification describes the quality of the act, whereas an excuse relates to the status or capacity (or lack of it) in the accused. "To exculpate" means to free a particular individual from culpability after he or she has caused loss or damage and to represent this in a judgment that is either an acquittal or mitigates sentencing in the criminal law, or reduces or extinguishes the liability to pay compensation to the victim in the civil law.

Explanation

The executive and legislative branches of modern states enact policy into laws which are then administered through the judicial system. Judges also have a residual discretion to excuse individuals from liability if it represents a just result. When considering the consequences which are to be imposed on those involved in the activities forming the subject matter of the common law or legislation, governments and judges have a choice:

the criminal or civil defendant may be excused from liability as belonging to a class of person that ought to be excused, their behaviour may be considered justified, or an exculpation may be allowed on the merits of the particular case.

To be excused from liability means that although the defendant may have been a participant in the sequence of events leading to the prohibited outcome, no liability will attach to the particular defendant because he or she belongs to a class of person exempted from liability. In some cases, this will be a policy of expediency. Hence, members of the armed forces, the police or other civil organizations may be granted a degree of immunity for causing prohibited outcomes while acting in the course of their official duties, e.g. for an assault or trespass to the person caused during a lawful arrest or for an ambulance driver exceeding the speed limit in an emergency. Others are excused by virtue of their status and capacity. Others may escape liability because the quality of their actions satisfied a general public good. For example, the willingness to defend oneself and others, or property from injury may benefit society at large. Albeit that the actions of a vigilante fall outside the formal controls that would seek to ensure reasonable use of force in state-appointed police officers, such people may accidentally find themselves interrupting the commission of a crime and their actions in defence of their own or another's interests is justified out of expediency as opposed to having to wait until a police officer arrives before help can be rendered.