Coercion is compelling a party to act in an involuntary manner by use of threats, including propaganda or force. It involves a set of various types of forceful actions that violate the free will of an individual to induce a desired response, for example: a bully demanding lunch money from a student or the student gets beaten. These actions may include extortion, blackmail, torture, threats to induce favors, or even sexual assault. In law, coercion is codified as a duress crime. Such actions are used as leverage, to force the victim to act in a way contrary to their own interests. Coercion may involve the actual infliction of physical pain/injury or psychological harm in order to enhance the credibility of a threat. The threat of further harm may lead to the cooperation or obedience of the person being coerced.

A mistake of fact may sometimes mean that, while a person has committed the physical element of an offence, because they were laboring under a mistake of fact, they never formed the mental element. This is unlike a mistake of law, which is not usually a defense; law enforcement may or may not take for granted that individuals know what the law is.

In the criminal law of many nations, necessity may be either a possible justification or an exculpation for breaking the law. Defendants seeking to rely on this defense argue that they should not be held liable for their actions as a crime because their conduct was necessary to prevent some greater harm and when that conduct is not excused under some other more specific provision of law such as self-defense. Except for a few statutory exemptions and in some medical cases there is no corresponding defense in English law for murder.

For example, a drunk driver might contend that they drove their car to get away from being kidnapped. Most common law and civil law jurisdictions recognize this defense, but only under limited circumstances. Generally, the defendant must affirmatively show (for example, introduce some evidence) that (a) the harm they sought to avoid outweighs the danger of the prohibited conduct they are charged with; (b) they had no reasonable alternative; (c) they ceased to engage in the prohibited conduct as soon as the danger passed; and (d) they themselves did not create the danger they sought to avoid. Thus, with the "drunk driver" example cited above, the necessity defense will not be recognized if the defendant drove further than was reasonably necessary to get away from the kidnapper, or if some other reasonable alternative was available to them.