I. Introduction

The interpretation and construction of penal laws in the Philippines sit at the intersection of constitutional guarantees, statutory text, and long-developed jurisprudence. Because criminal statutes deal with life, liberty, and reputation, the legal system applies distinctive—often stricter—rules to their interpretation than to ordinary civil or administrative laws.

At the core lie a few recurring ideas:

No one may be punished under a vague, uncertain, or retroactive penal law.
Doubts are resolved in favor of the accused.
Courts cannot create crimes or penalties by analogy, implication, or equitable reasoning; they must find them in the statute itself.
All of this is anchored in the Constitution’s protections of due process and against ex post facto laws and bills of attainder.

This article outlines the main principles, their bases, and how they operate in practice within the Philippine legal system.

II. Constitutional and Statutory Foundations

A. Constitutional guarantees

Three constitutional pillars shape the interpretation of penal laws:

Due process of law
- Article III, Section 1 of the 1987 Constitution provides that no person shall be deprived of life, liberty, or property without due process of law.
- Due process in the penal context requires:
  - A valid, clear law defining the punishable act and penalty.
  - Fair notice and opportunity to comply.
  - Fair procedures in prosecution and adjudication.
Prohibition of ex post facto laws and bills of attainder
- Article III, Section 22 prohibits:
  - Ex post facto laws — laws that criminalize past conduct that was innocent when done, or increase the penalty or burden for an act already committed.
  - Bills of attainder — legislative acts that directly inflict punishment without judicial trial.
- This prohibition drives the principle that penal laws are generally prospective and that courts must be cautious not to interpret statutes in ways that effectively make them retroactive or punitive without basis.
Equal protection and other rights
- Equal protection constrains discriminatory or arbitrary classifications in penal statutes.
- Other rights—against unreasonable searches and seizures, self-incrimination, cruel punishment, etc.—influence how criminal laws are enforced and interpreted (for example, exclusion of illegally obtained evidence).

B. Statutory foundations: Revised Penal Code and Civil Code

Revised Penal Code (RPC) The RPC is the primary source of general penal principles and crimes (felonies). It provides:
- General principles (Book I): territoriality, generality, prospectivity, stages and degrees of execution, circumstances affecting liability, etc.
- Specific felonies (Book II).
Civil Code provisions on application and interpretation of laws
- Article 4: Laws shall have no retroactive effect, unless the contrary is provided.
- Article 10: In case of doubt in the interpretation or application of laws, it is presumed that the lawmaking body intended right and justice to prevail.
These general rules apply suppletorily to penal laws, subject to the specialized doctrines of criminal law and the explicit rule on favorable retroactivity in the RPC.
Article 22, Revised Penal Code – Retroactivity of favorable penal laws
- As an exception to the general rule of prospectivity, Article 22 provides that penal laws shall have retroactive effect insofar as they favor the accused, who is not a habitual delinquent, even if final judgment has been rendered and he is serving sentence.
- This provision is central to how courts handle amendatory laws that lower penalties, reclassify crimes, or decriminalize conduct.

III. Distinctive Principles of Penal Law Interpretation

1. Strict construction of penal laws (Rule of lenity)

General rule: Penal laws are strictly construed against the State and liberally in favor of the accused.

The State, in wielding its power to punish, must do so under clear, unequivocal laws.
If, after applying accepted methods of interpretation, a genuine, irreconcilable doubt remains as to:
- Whether an act falls within the crime defined, or
- Which of two possible penalties should apply, the doubt is resolved in favor of the accused.

Consequences of strict construction:

Courts cannot broaden the scope of criminal liability by:
- Analogy (comparing to similar crimes).
- Implication or conjecture.
- Appeals to public policy or morality alone.
Penal statutes must be read as written, and their coverage cannot be extended to acts not clearly included.

This is sometimes referred to as the rule of lenity: when language is ambiguous, interpretation leans toward leniency.

2. In dubio pro reo (in doubt, for the accused)

This principle has both interpretative and evidentiary dimensions:

Interpretative: When the meaning or application of a penal statute remains doubtful even after applying ordinary canons, the doubt favors the accused.
Evidentiary: If, after trial, there remains reasonable doubt as to the guilt of the accused, the court must acquit.

While the evidentiary rule relates to proof, the interpretative aspect directly shapes how statutes are read. Courts must avoid interpretations that resolve ambiguities in favor of harsher criminal liability.

3. Nullum crimen, nulla poena sine lege (no crime, no penalty without law)

This classical principle dictates that:

No act or omission is a crime unless made so by law in force before its commission.
No penalty may be imposed unless it is prescribed by law for the act charged.

In practical terms:

Courts cannot create crimes based on moral notions, custom, or presumed legislative intent without a statutory foundation.
Administrative issuances, circulars, and regulations cannot independently create crimes or penalties; they must be anchored on a law that clearly defines the offense and authorizes sanctions.
Vague or overly broad statutes may be struck down or narrowly construed to avoid unconstitutional uncertainty.

4. No penal liability by analogy or extensive interpretation to the detriment of the accused

Penal statutes cannot be extended by analogy to cover acts not clearly within their terms if doing so would be unfavorable to the accused.
However, analogy may be allowed when it operates in favor of the accused (e.g., by extending the benefit of a mitigating or exempting circumstance).

This is a key limit on judicial creativity: criminal liability must rest on clear statutory language, not judicial innovation.

IV. General Canons of Statutory Construction Applied to Penal Laws

Although penal statutes are special, they are still laws and subject to general canons of interpretation, with criminal-specific modifiers.

1. Verba legis and ratio legis

Verba legis (plain meaning): When the law is clear, the duty of the court is to apply it, not to interpret it.
Ratio legis (spirit or reason of the law): When literal interpretation leads to absurdity, injustice, or contradicts the overall purpose, courts may consider the law’s spirit.

In penal law:

Courts start with the text; textual clarity normally controls.
Appeals to the “spirit” are used cautiously, and rarely to expand criminal liability.
Purpose-based interpretation may reasonably confine or soften a penal provision to avoid unconstitutional or unjust results.

2. Ejusdem generis, noscitur a sociis, expressio unius, etc.

These traditional canons are frequently applied in criminal cases:

Ejusdem generis: Where general words follow particular and specific words, the general words are limited to the same kind as those specifically mentioned.
- Example: If a statute penalizes carrying “pistols, revolvers, rifles, or other deadly weapons,” “other deadly weapons” will be read as similar to firearms.
Noscitur a sociis: A word is known by the company it keeps; ambiguous terms draw meaning from the surrounding words and context.
Expressio unius est exclusio alterius: Express mention of one thing implies the exclusion of others not mentioned.
- For example, if a law penalizes specific roles (e.g., public officers) and does not include private persons, courts avoid reading private persons into the coverage unless clearly intended.

In penal interpretation, these canons tend to narrow rather than broaden liability.

3. Article 10 of the Civil Code and its penal relevance

Article 10’s presumption that the legislature intended “right and justice” supplements penal interpretation:

When multiple plausible interpretations exist, courts lean toward those that:
- Uphold constitutional rights,
- Avoid harsh or disproportionate penalties,
- Promote fairness and humane treatment.

However, this principle cannot justify creating new crimes or expanding liability where the statute is silent.

V. Special Topics in Penal Interpretation

A. Mala in se vs. mala prohibita

Philippine jurisprudence distinguishes:

Mala in se (wrongs in themselves, e.g., murder, theft)
- Governed primarily by the RPC.
- Criminal intent (dolo) is generally required.
- Good faith and lack of intent can be significant in excluding or reducing liability.
Mala prohibita (acts criminal because prohibited, usually under special laws)
- Often regulatory or public welfare statutes, e.g., traffic, environmental, economic, and special regulatory laws.
- Criminal intent is often not required beyond the intent to commit the prohibited act.
- Mere commission of the act—regardless of malice—may be sufficient.

Interpretation consequences:

For mala in se, courts are more inclined to require proof of intent and may interpret provisions in light of moral blameworthiness.
For mala prohibita, courts emphasize clear statutory text and the legislature’s regulatory purpose; however, they still apply the rule that ambiguities are resolved in favor of the accused.
Even in mala prohibita, where elements are unclear or penalties uncertain, strict construction still applies.

B. Interpretation of qualifying, aggravating, and mitigating circumstances

Qualifying circumstances
- Transform the nature of the crime (e.g., homicide to murder).
- Must be:
  - Expressly alleged in the information, and
  - Proved beyond reasonable doubt.
- They are strictly construed; if doubt exists as to their presence, the accused is convicted only of the lesser offense.
Generic aggravating circumstances
- Increase the penalty within the range prescribed by law but do not change the nature of the crime.
- Also strictly construed and must be clearly proven.
Mitigating circumstances
- May lower the penalty within or below the prescribed range.
- Courts are more liberal in appreciating them, and ambiguities are often resolved in favor of recognizing mitigation, consistent with the pro reo principle.

C. Special penal laws and their construction

Special penal laws (e.g., anti-graft, dangerous drugs, economic and environmental laws) are interpreted with attention to:

Legislative purpose — often to curb specific social evils.
Textual clarity — due to the strict construction rule, elements must be clearly defined.
Relationship with the RPC — the RPC often supplies general principles, but many special laws contain their own specific rules on penalties, stages of execution, and liability.

Where special laws are silent, courts may apply RPC principles suppletorily, but not in a way that increases criminal liability beyond what the special statute reasonably contemplates.

D. Administrative regulations and penal sanctions

Administrative agencies may issue implementing rules that clarify how a penal law is applied (e.g., defining standards, procedures, classifications).
However, they cannot create crimes or penalties beyond what the enabling law allows.
If a regulation appears to broaden criminal liability or impose harsher sanctions than the statute, courts interpret it narrowly or invalidate it.

VI. Retroactivity, Prospectivity, and Transitional Issues

A. General rule: Prospectivity of penal laws

Under Article 4 of the Civil Code and constitutional prohibition of ex post facto laws, penal statutes generally apply only to acts committed after they take effect.
Courts avoid interpretations that punish past conduct not clearly covered at the time it was done.

B. Favorable retroactivity: Article 22, RPC

Article 22 carves out the crucial exception:

A penal law that is favorable to the accused has retroactive effect, even if:
- The act was committed before its enactment, and
- Final judgment has become executory and the accused is serving sentence.

Examples of favorable changes:

Reduction in penalties.
Reclassification of crimes to less serious categories.
Decriminalization or repeal of the penal provision.

Practical applications:

When a new law reduces penalties, courts or penal authorities re-compute sentences or order release if the reduced maximum is already served.
When an act is decriminalized, ongoing prosecutions are dismissed, and those convicted may be released and their criminal liability extinguished.

Limitations:

Typically, the benefit is not extended to habitual delinquents, consistent with Article 22.
Favorable retroactivity does not revive a case already fully served simply to “clean” the historical record; however, it can affect ongoing punishment and collateral consequences.

C. Procedural vs. substantive penal changes

Substantive penal laws (defining crimes and penalties) generally do not apply retroactively if prejudicial, but do retroact if favorable (Article 22).
Procedural/remedial changes (e.g., rules of evidence, prescription, jurisdiction) are generally retroactive as they are considered to affect modes of enforcing rights rather than the substantive rights themselves—subject always to due process.

VII. Interpretation in Light of Constitutional Rights and Doctrines

A. Overbreadth and vagueness

Penal laws must be sufficiently clear so that:
- Ordinary persons can understand what conduct is prohibited; and
- Law enforcement has minimal discretion, avoiding arbitrary and discriminatory enforcement.

Vague or overbroad statutes may be:

Struck down as unconstitutional, or
Narrowly construed to save them, provided such narrowing remains faithful to legislative intent and does not amount to judicial rewriting.

B. Presumption of constitutionality vs. strictness of penal statutes

Laws are presumed constitutional, but in penal statutes, this presumption is tested against:
- Due process,
- Equal protection,
- Freedom of expression and association,
- Rights of the accused in criminal proceedings.

When penal laws touch on fundamental rights (e.g., speech, assembly), courts may apply strict scrutiny or similar heightened review, which influences how they interpret and, if necessary, limit the reach of the statute.

VIII. Limits of Equitable and Policy-Based Reasoning

Unlike civil law, where courts sometimes rely on equity and broader notions of fairness to fill gaps, in penal law:

Equity does not create crimes or penalties.
Courts cannot:
- Impose punishment simply because conduct seems morally wrong or socially harmful, absent a clear statute.
- Increase penalties or expand coverage by appealing to public policy or convenience alone.

However:

Equity and humanitarian considerations may influence:
- Interpretation of ambiguous provisions in favor of the accused.
- Choice among multiple permissible applications of mitigating rules, probation, or penalties within a range.

IX. The Role of Information, Allegations, and Proof in Construction

Interpretation of penal statutes is closely linked to criminal procedure:

Allegation in the information
- Every element of the offense, including qualifying and aggravating circumstances, must be alleged in the charge.
- Even if the law clearly defines an aggravating or qualifying circumstance, it cannot be used to increase liability if not properly alleged.
Proof beyond reasonable doubt
- Statutory elements and qualifying/aggravating circumstances must be proven beyond reasonable doubt.
- Ambiguities in the evidence (e.g., doubt as to whether a deadly weapon was used, or whether the act falls within the timing or place required) are resolved in favor of the accused.
Interpretation of composite and continuing crimes

Courts have had to interpret:
- Complex crimes (e.g., robbery with homicide, rape with homicide, etc.): Whether a series of acts constitute one complex crime or several separate offenses depends on statutory language and intent, resolved strictly.
- Continuing offenses: Some statutes treat conduct as continuing (e.g., illegal possession). Interpretation of when the offense is consummated affects prescription, venue, and liability, and must adhere closely to legislative text and intent.

X. Synthesis and Conclusion

Philippine penal law interpretation is guided by a consistent, overarching theme: the criminal law is a last-resort, coercive instrument that must be written and applied with exceptional clarity and caution.

Key takeaways:

Strict construction: Penal statutes are construed strictly against the State and liberally in favor of the accused. Doubts in interpretation and application are resolved pro reo.
Legality principle: No crime and no penalty exist without prior, clear law. Courts cannot create or extend penal liability by analogy, implication, or equity.
Constitutional guardrails: Due process, prohibitions on ex post facto laws and bills of attainder, and other fundamental rights shape and limit how penal laws can be written and applied.
Prospectivity with a humane exception: Penal laws generally apply prospectively, but Article 22 of the RPC mandates retroactivity for those favorable to the accused, reflecting the humane orientation of Philippine criminal justice.
Integration with general canons: Traditional rules of statutory construction—verba legis, ejusdem generis, noscitur a sociis, expressio unius, etc.—are used, but always filtered through the harsher scrutiny appropriate to criminal statutes.
Special considerations:
- The distinction between mala in se and mala prohibita affects how courts treat intent and good faith.
- Qualifying and aggravating circumstances are strictly alleged and proven.
- Special laws and administrative regulations must stay within the boundaries of the enabling penal statutes.

In sum, the Philippine approach to penal interpretation aims to protect individual liberty, prevent legislative and executive overreach, and ensure fairness in the imposition of criminal liability—without abandoning the State’s legitimate interest in punishing genuine social harms.