Fundamentals

Legality: What It Means and Why It Limits Power

By Daniel Sardá · Published on September 23, 2026

6 min read1,174 words

Legality requires public authority to act on a legal basis, within its powers, and through procedures open to review.

An authority denies a permit, imposes a fine, or collects a tax. Before asking whether the decision is sensible, a more basic question arises: what rule authorizes it, and how far does that authority extend? That question leads to the principle of legality.

In its broadest sense, legality means conformity with the law in force. Applied to public power, it requires something more specific: every official act must have a legal basis, be taken by the competent authority, and follow the established procedure. Those who exercise power cannot create powers for themselves case by case or decide solely according to their own will.

Key idea: Legality does not require public authorities to stand still; it requires them to justify what they do in legal terms.

From obeying rules to the principle of legality

In everyday language, saying that conduct is legal usually means that it is not prohibited or that it complies with the applicable rules. In public law, the principle of legality has an institutional function: it binds state bodies to the legal order that defines their powers.

That does not mean every decision is specified in advance down to the last detail. Many authorities have room to assess circumstances and choose among several responses. But discretion is not the same as unlimited freedom. It must have a legal basis, be exercised within defined limits, and remain open to review.

The Venice Commission, in its rule-of-law checklist, links legality to legal authorization for state action, defined powers, and the possibility of reviewing their exercise. This is a guiding framework, not a universally binding rule, but it expresses a widely recognizable idea: anyone exercising public power should be able to explain where that authority comes from.

Why legality protects against arbitrariness

Legality turns an order into a decision that can be examined. It allows us to ask whether the authority:

• had the power to act;
• applied the relevant rule;
• followed the required procedure;
• respected the limits of its discretion;
• gave reasons that can be reviewed.

Imagine that an office denies a permit because an official adds a requirement absent from the applicable rules. Even if the office has authority over those permits, its decision may be unlawful if it rests on a criterion invented for that case. Legality protects here not because it automatically guarantees a favorable result, but because it prevents authorities from changing the conditions without legal grounds.

This function is related to the generality of the law: general rules reduce the scope for privileges and burdens designed for particular people. It also helps identify abuse of authority, which can arise when a public body exceeds the powers assigned to it.

Legality is not justice, legitimacy, or the rule of law

A rule may have been enacted and applied according to the proper procedure and still be unjust, disproportionate, or contrary to fundamental rights. It is therefore useful to keep several questions separate.

Legality asks whether conduct or a decision conforms to the legal order. Legitimacy asks whether power and its decisions deserve acceptance or rest on sufficient political justification. Morality assesses what is right or wrong according to ethical reasons. The answers may coincide, but none replaces the others.

Nor are legality and the rule of law synonyms. Legality is an indispensable part of that broader framework, which also includes the protection of rights, equality before the law, checks on abuses of power, and access to independent justice. A government may produce many rules and formally follow some procedures while retaining powers so broad, or controls so weak, that arbitrariness endures.

Essential distinction: Calling a measure legal describes its relationship to the law in force; it does not by itself show that the measure is just, legitimate, or compatible with a genuine rule of law.

How it operates in administration, taxation, and criminal law

In public administration, legality requires every body to act within the powers assigned to it. A health, municipal, or regulatory authority cannot assume another body's powers, and its decisions must follow the applicable procedures. Where the law permits several options, reasoned decisions and review help show that the choice was not arbitrary.

In taxation, the principle prevents an official from unilaterally inventing a payment obligation. The precise scope of the requirement that taxation rest on legislation—what elements must be set out in a formal statute and which may be developed through other rules—depends on the legal system concerned. There is no identical formula for every country.

The principle of legality in criminal law imposes especially strict safeguards because the power to punish is at stake. Put simply, no one should be convicted for conduct that was not a crime when it occurred, or receive a more severe penalty retroactively. Article 15 of the International Covenant on Civil and Political Rights and Article 9 of the American Convention on Human Rights set out these safeguards and recognize the benefit of a later, lighter penalty where they apply.

The requirement of specificity complements this protection: prohibited conduct and its consequence must be defined with sufficient precision. If a person is punished through an unforeseeable expansion of a rule or by analogy to that person's detriment, the ability to know in advance what is prohibited is weakened.

Public, foreseeable, and reviewable rules

A secret or inaccessible rule can hardly guide conduct. A rule so vague that it permits any outcome likewise provides no effective constraint. For that reason, legality is connected to legal certainty: people need a reasonable opportunity to know the rules and foresee their consequences.

Publication, accessibility, a measure of stability, and sufficiently clear drafting are among the conditions that reinforce that predictability. They are not absolute requirements, nor do they operate identically in every field. Rules can change, and applying them requires interpretation. What matters is that those changes and that interpretation do not turn the law into a surprise manufactured after the fact.

Review completes the principle. If there is no way to challenge a decision, examine the authority's competence, or require a justification, the appeal to legality risks remaining only a declaration. Administrative and judicial review make it possible to compare a particular act with the rules said to support it.

Key idea: Predictability limits power before it acts; review makes it possible to examine power afterward.

A necessary, though insufficient, safeguard

Legality sets the starting point for all limited government: no public decision is justified merely because someone has the material ability to impose it. It must rest on known rules, come from an identifiable authority, and be open to review.

That standard does not itself settle whether a law is good or secure every condition of a free society. But it makes it possible to ask verifiable questions of power: who may decide, on what grounds, through which procedure, and subject to what review? Its institutional value lies there: replacing occasional will with legal reasons that citizens can know and challenge.