Legal certainty

Legal certainty is the quality of law that makes rules sufficiently clear, stable, and predictable for people to guide their conduct and anticipate legal consequences.

Rule of law: The principle that public power must be exercised under law, with officials and citizens subject to legal constraints. Legal certainty is one of the rule of law’s central requirements.
European Court of Human Rights: An international court that adjudicates alleged violations of the European Convention on Human Rights. Its judgments assess whether legal rules let people foresee their consequences.
Legal indeterminacy: The condition in which legal materials leave multiple plausible outcomes or lack a determinate answer. It marks the uncertainty legal certainty seeks to limit, not necessarily eliminate.
Legal transition: The process of moving from one legal regime or set of rules to another. Transition provisions can preserve predictability when laws change.
Legal predictability: The degree to which people can foresee how legal rules will apply to conduct and disputes. Predictability is the practical test of whether law can guide conduct.
Article 7 of the European Convention on Human Rights: The Convention provision prohibiting punishment without law, including retroactive criminal penalties. It applies foreseeability and non-retroactivity requirements to criminal law.
Judicial discretion: The authority of judges to choose among legally permissible outcomes when applying law to cases. Broad discretion can make outcomes harder to predict, though it may support fairness.
Grandfather clause: A provision that exempts existing activities or circumstances from a new legal requirement. It can protect established reliance while a new rule takes effect.
Clarity (law): The quality of a legal rule whose meaning and scope can be understood without undue ambiguity. Clear wording helps people identify what conduct a rule permits or forbids.
Sunday Times v United Kingdom: A 1979 European Court of Human Rights case concerning a contempt-of-court injunction and freedom of expression. The Court explained that law must be accessible and foreseeable.

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