"Nullum crimen sine lege": How strictly does Japan uphold the principle of legality in criminal law?

The principle of nullum crimen, nulla poena sine lege – "no crime, no punishment without law" – is a cornerstone of modern criminal justice systems worldwide, serving as a fundamental safeguard for individual liberty against arbitrary state power. In Japan, this doctrine, known as Zai Kei Hōtei Shugi (罪刑法定主義), is not merely an academic concept but a constitutionally entrenched principle that profoundly shapes the creation, interpretation, and application of criminal law. This article explores the contours of Zai Kei Hōtei Shugi, examining its core components and the rigor with which it is upheld in the Japanese legal system.

The Bedrock: What is the Principle of Legality (Zai Kei Hōtei Shugi) in Japan?

At its essence, Zai Kei Hōtei Shugi embodies the idea that an act can only be deemed criminal, and punishment imposed, if a law enacted prior to the commission of the act explicitly defined it as such and prescribed a penalty. This principle is deeply rooted in both democratic and liberal ideals.

• Democratic Foundation: It reflects the democratic conviction that only the people, through their elected representatives in the Diet (Japan's parliament), have the legitimacy to determine what conduct warrants criminal sanction. This prevents the executive or judicial branches from unilaterally creating crimes.
• Liberal Foundation: It serves as a critical guarantee of individual freedom by ensuring legal certainty and predictability. Citizens must be able to ascertain in advance what conduct is prohibited, allowing them to regulate their actions accordingly and avoid unforeseen criminal liability. This protects against the arbitrary exercise of state power.

The Japanese Constitution provides a robust framework for Zai Kei Hōtei Shugi through several articles:

• Article 31: "No person shall be deprived of life or liberty, nor shall any other criminal penalty be imposed, except according to procedure established by law." This "procedure established by law" encompasses not only procedural due process but also the substantive requirement that the criminal law itself be duly established.
• Article 39: "No person shall be held criminally liable for an act which was lawful at the time it was committed..." This directly prohibits retroactive criminalization.
• Article 73, Paragraph 6, Proviso: Cabinet orders (a form of executive regulation) cannot include penal provisions unless specifically authorized by law.

From these constitutional mandates flow several key sub-principles that give practical effect to Zai Kei Hōtei Shugi.

1. "By Law Alone" - The Principle of Statutory Law (Hōritsu Shugi)

The first and foremost implication of Zai Kei Hōtei Shugi is that criminal offenses and their corresponding penalties must be defined by statutes enacted by the Diet.

• The Diet's Exclusive Role: The power to create criminal law rests exclusively with the national legislature. This principle, Hōritsu Shugi, underscores the democratic legitimacy of criminal norms.
• Limits on Delegation to the Executive: While laws can delegate authority to executive bodies to issue orders and regulations, this power is strictly limited concerning penal sanctions. Article 73, Paragraph 6 of the Constitution permits penal provisions in cabinet orders only with "specific delegation" from a statute. A general, sweeping delegation is impermissible; the authorizing law must clearly define the scope and nature of the conduct that can be penalized by administrative regulation.
  The Supreme Court of Japan has affirmed this, requiring "specific and concrete delegation" for administrative bodies to establish penal rules. A landmark case, the Sarufutsu Case (Supreme Court ruling of November 6, 1974), addressed the constitutionality of delegating the power to define prohibited "political acts" for public servants to the National Personnel Authority. The Court found the delegation permissible, reasoning that the scope of "political acts" that could undermine the political neutrality of public servants was reasonably discernible from the National Public Service Act itself.
• Local Ordinances and Penal Provisions: Local public entities (prefectures and municipalities) can enact ordinances and include penal provisions (e.g., imprisonment for not more than 2 years, fines of not more than 1 million yen) under Article 14 of the Local Autonomy Act, provided they do not conflict with national laws. While this appears to be a broader delegation than allowed for the national executive, it is justified by the democratic legitimacy of local assemblies, whose members are directly elected by residents. The Supreme Court, in the Tokushima City Public Safety Ordinance Case (Supreme Court ruling of September 10, 1975), upheld the constitutionality of such local penal provisions, likening ordinances passed by elected local assemblies to laws passed by the Diet in terms of their democratic basis, and requiring only that the legislative authorization be "reasonably specific and limited".
• The Judiciary's Role: Courts are bound by enacted statutes. They cannot create new crimes through judicial precedent (judge-made law) or by invoking customary law. Their role is to interpret and apply existing statutory criminal law.

2. The Shield of Predictability - The Prohibition of Ex Post Facto Laws (Jigo Hō no Kinshi)

A critical corollary of Zai Kei Hōtei Shugi is the strict prohibition against retroactive criminal laws, or ex post facto laws. This principle is explicitly enshrined in Article 39 of the Constitution: "No person shall be held criminally liable for an act which was lawful at the time it was committed, or of which he has been acquitted, nor shall he be placed in double jeopardy."

• No Punishment for Past Lawful Acts: If an act was not defined as a crime when it was performed, it cannot be made criminal and punished retrospectively by a subsequently enacted law. This ensures that individuals can rely on the law as it exists at the time of their actions.
• Prohibition of Retroactive Aggravation of Penalties: Beyond criminalizing previously lawful conduct, this principle also generally prohibits the retroactive application of harsher penalties. If a law is amended after an offense is committed to increase the punishment for that offense, the more severe penalty cannot be applied to the past act. Article 6 of the Penal Code of Japan stipulates, "When the punishment is changed by a law enacted after the commission of a crime, the lesser punishment shall be applied". This provision ensures that an offender benefits from any subsequent legislative leniency.
• Changes in Judicial Interpretation: A more complex issue arises when judicial interpretation of a criminal statute changes over time. If a court reinterprets a law in a way that is disadvantageous to a defendant (e.g., by broadening the scope of criminalized conduct), applying this new interpretation retroactively could undermine predictability. While Article 39 of the Constitution directly addresses legislative changes, its application to judicial reinterpretations is less direct. The Supreme Court of Japan has held that applying a new, disadvantageous judicial interpretation retroactively does not, in itself, violate Article 39 (Supreme Court ruling of November 18, 1996). However, in such cases, a defendant who acted in reliance on a previously established, more lenient interpretation might, depending on the circumstances, argue a lack of culpability due to an unavoidable mistake regarding the scope of the law (an issue related to "awareness of illegality," discussed under the Principle of Culpability).

3. Interpretation with Caution - The Ban on Analogical Interpretation (Ruizui Kaishaku no Kinshi)

To prevent the judiciary from effectively creating new crimes and thereby usurping the legislative function, Zai Kei Hōtei Shugi prohibits the analogical interpretation (類推解釈, ruizui kaishaku) of criminal statutes to the detriment of the accused. If an act does not fall squarely within the definition of a crime as written, a court cannot extend the definition by analogy to cover similar but distinct conduct, even if that conduct seems equally blameworthy.

• Distinguishing Permissible Broad Interpretation (Kakuchō Kaishaku): This ban on analogy must be distinguished from permissible "broad interpretation" or "expansive interpretation" (拡張解釈, kakuchō kaishaku). Broad interpretation involves construing the words of a statute according to their possible, albeit wide, linguistic meaning to cover a specific act. The line between permissible broad interpretation and impermissible analogy can be fine and is a frequent subject of legal debate. The key difference lies in whether the interpretation remains within the possible textual meaning of the statute or steps outside it to punish conduct not covered by the statutory language.
• The "Electricity Theft" Case: A classic example often cited to illustrate permissible broad interpretation is the Daishin-in (Great Court of Cassation, Japan's highest court before World War II) ruling of May 21, 1903, concerning the theft of electricity. At the time, the Penal Code defined theft in terms of "movable property." The Court held that electricity, though intangible, could be managed and was subject to exclusive possession, thus falling under a broad interpretation of "movable property" for the purposes of theft. (The current Penal Code, Article 245, explicitly deems electricity to be property in the context of theft and robbery, reflecting a legislative endorsement of this outcome ).
• Rationale: The prohibition of analogy ensures that criminal liability is based on the clear text of the law, not on a judge's subjective view of what should be criminal. It forces the legislature to be precise in drafting criminal statutes.

4. Clarity is Key - The Principle of Clarity (Meikakusei no Gensoku)

Even if a law is duly enacted and not applied retroactively, it can still violate Zai Kei Hōtei Shugi if its provisions are excessively vague or unclear. This is known as the Principle of Clarity (明確性の原則, meikakusei no gensoku), sometimes referred to in Anglo-American law as the void-for-vagueness doctrine.

• Vague Laws are Void: A penal statute that is so vague that individuals of common intelligence must necessarily guess at its meaning and differ as to its application fails to provide fair notice of what conduct is prohibited. Such a law is unconstitutional, typically under Article 31 (due process). It effectively delegates law-making authority to the police, prosecutors, and courts, who are left to apply their own interpretations on an ad hoc basis.
• The "Ordinary Person of Reasonable Intelligence" Standard: The Supreme Court of Japan, in the Tokushima City Public Safety Ordinance Case (Supreme Court ruling of September 10, 1975), established that the test for clarity is whether the statute's language, as understood by an "ordinary person of reasonable intelligence" (通常の判断能力を有する一般人, tsūjō no handan nōryoku o yūsuru ippanjin), provides an ascertainable standard for determining what conduct falls within its scope. The statute must enable such a person to distinguish between prohibited and permissible conduct.
• The Chilling Effect: Vague penal statutes can have a "chilling effect" on legitimate activities, as individuals may steer far wider of the unlawful zone than if the boundaries were clearly drawn, for fear of accidentally transgressing an ambiguous prohibition. This is particularly problematic in areas involving fundamental rights, such as freedom of expression.
• Case Study: The "Immoral Conduct" (Inkō) Provision: The Fukuoka Prefecture Youth Protection and Upbringing Ordinance Case (Supreme Court ruling of October 23, 1985) provides an important example. The ordinance penalized "immoral conduct" (inkō) with minors. Critics argued that "inkō" was unconstitutionally vague. The Supreme Court, however, upheld the provision by narrowly construing "inkō" to refer to sexual acts that exploit the immaturity of minors or treat them merely as objects of sexual gratification, deeming this interpretation understandable by the ordinary person. This demonstrates the judiciary's practice of, where possible, giving a clarifying (and often narrowing) construction to potentially vague statutes to save them from unconstitutionality.

5. Fairness in Substance - Substantive Appropriateness and Proportionality

Beyond formal requirements, Zai Kei Hōtei Shugi is increasingly understood to encompass demands for substantive fairness in criminal legislation.

• Prohibition of Criminalizing Harmless Acts: A law that penalizes conduct which causes no harm to any protected legal interest may be deemed an unjustifiable infringement on liberty. The Supreme Court touched upon this in the HS-style non-thermal high-frequency therapy case (Supreme Court ruling of January 27, 1960). The case involved a law prohibiting unlicensed medical-like practices. The Court interpreted the law to apply only to practices that posed a "risk of harm to human health," thus excluding harmless activities from its ambit through a constitutionally informed restrictive interpretation.
• Avoiding Overly Broad Criminalization: Penal statutes must not be so broad as to unduly restrict legitimate activities or fundamental rights. If a law sweeps too broadly, it may be challenged for infringing on rights protected by the Constitution, even if it is not vague. Again, courts may attempt to narrow such statutes through interpretation, as seen in the Fukuoka Prefecture youth protection case mentioned above.
• Proportionality between Crime and Punishment (Zai Kei no Kinkō): There must be a reasonable balance or proportionality between the gravity of the offense and the severity of the prescribed punishment. A grossly disproportionate penalty may be unconstitutional. The most prominent example is the Supreme Court's ruling of April 4, 1973, which declared the aggravated punishment for parricide (killing one's own lineal ascendant) under the old Penal Code Article 200 unconstitutional as a violation of the equality principle (Article 14 of the Constitution) due to its extreme severity compared to ordinary homicide. While this case was decided on equality grounds, the underlying concern for proportionality is evident.

How Strictly is "Strictly Upheld"? Nuances and Challenges

Japan demonstrates a strong commitment to Zai Kei Hōtei Shugi and its derivative principles. Constitutional provisions and a body of case law consistently reinforce these safeguards. However, the application of these principles is not without its nuances and challenges:

• Balancing Legal Certainty with Evolving Society: The need for legal certainty can sometimes clash with the necessity of addressing new forms of harmful conduct emerging from technological or social changes (e.g., cybercrime, complex financial fraud). The legislature may struggle to keep pace, and courts face the delicate task of interpreting existing laws in light of new realities without overstepping into impermissible analogy or vagueness.
• The Role of Judicial Interpretation: While courts cannot create crimes, their interpretative function is crucial. The line between legitimate expansive interpretation and prohibited analogical interpretation, or between a saving construction and judicial legislation, can be a source of ongoing debate and requires careful judicial craftsmanship.
• Delegated Legislation: The extent to which penal rulemaking can be delegated to administrative bodies, even with "specific delegation," remains a sensitive issue, requiring a balance between legislative supremacy and administrative efficiency.

In conclusion, Zai Kei Hōtei Shugi is a vital and rigorously applied principle in Japanese criminal law. It serves as a fundamental bulwark for individual and corporate freedom by demanding that criminal liability be based only on clear, pre-existing, and democratically enacted laws, interpreted strictly, and applied fairly and proportionately. While challenges in its application persist, particularly in a rapidly changing society, the commitment to these ideals remains a defining feature of the Japanese criminal justice system, providing a crucial element of predictability and protection against arbitrary state action.