# The Principle of Legality

Law I · Foundations of Criminal Law and the Theory of the Offence · https://tryals.app/learn/law-i/the-principle-of-legality

## Nullum Crimen, Nulla Poena Sine Lege

Feuerbach's formula sets the firmest limit on the power to punish. In **Spain**, Article 25.1 CE and Article 1.1 CP embed this guarantee.

### Four guarantees

The principle breaks into four distinct guarantees:

| Guarantee | Content |
|---|---|
| **Criminal** | No conduct is an offence without a prior statute |
| **Penal** | No penalty may be imposed unless fixed by statute |
| **Jurisdictional** | Penalties require a competent court and due process |
| **Enforcement** | Sentences must follow lawful execution rules |

### Requirements of the statute

The underlying statute must satisfy four conditions:

* **Lex praevia**: the law must precede the conduct. Laws that **favour** the accused **do** have retroactive effect under Article 2.2 CP.
* **Lex scripta**: the law must be written statute. Penalties restricting fundamental rights require an **organic** law.
* **Lex stricta**: judges must apply criminal laws strictly. This bars **analogy** against the accused, though the Code allows an analogical **mitigating** circumstance.
* **Lex certa**: provisions must be clear and precise. This duty binds the **legislator**, not merely the trial judge.

### Non bis in idem

No one may be punished twice for the same wrongful act. The Constitutional Court derived this rule directly from Article 25.1 CE.

The prohibition applies when **three** elements coincide:

* The same **subject**
* The same **facts**
* The same **foundation** (the legal interest protected)

Dual sanctions are barred if they share the same legal interest. In practice, criminal trials take precedence over administrative proceedings for identical facts.

> **Common pitfall:** stating that criminal law is never retroactive. It is never retroactive **against** the accused. Milder reforms apply retroactively to existing sentences.

## Practice questions

10 of this lesson's 14 practice questions, with answers. The full set is in the app.

### 1. Arrange these statements of the principle of legality in chronological order.

**Answer:**

1. The French Declaration of the Rights of Man and of the Citizen, 1789
2. Feuerbach coins nullum crimen, nulla poena sine lege, 1801
3. The Universal Declaration of Human Rights, 1948
4. The European Convention on Human Rights, 1950
5. The Spanish Constitution, 1978

**Why:** Two centuries of restatement is itself an argument. A limit that reappears in a revolutionary declaration, a scholar's textbook, a post-war universal instrument, a regional treaty and a national constitution is not a technicality of drafting; it is treated as a condition of a legal order that punishes at all.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/arrange-these-statements-of-the-principle-of-legality-in

### 2. Why is it consistent to forbid retroactive criminal law and at the same time apply a later, milder law to conduct already committed?

A. Defendants have an autonomous constitutional right to waive non-retroactivity whenever it is advantageous
B. Non-retroactivity protects advance notice of offences, which a milder subsequent law does not undermine
C. Favourable statutory reforms are treated as procedural rules rather than substantive criminal penalties
D. Retroactive application is mandatory when an amending statute formally repeals the prior offence fully

**Answer:** B. Non-retroactivity protects advance notice of offences, which a milder subsequent law does not undermine

**Why:** Because the guarantee is **one-directional by design**. It exists so that nobody is punished for conduct they could not have known was forbidden, or more heavily than the law then announced. A later law that reduces the penalty offends neither concern, which is why Article 2.2 CP makes it retroactive even against a final judgment.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/why-is-it-consistent-to-forbid-retroactive-criminal-law-and-at-the

### 3. The requirement of lex certa binds the legislator rather than the trial judge. Why does this distinction matter for the separation of powers?

A. It leaves the definition of offences entirely to the discretion of trial courts
B. It allows the judiciary alone to adapt penal definitions to novel social harms
C. It ensures that courts draft precise penal provisions whenever statutes fail
D. It prevents judges from defining criminal conduct through vague statutory terms

**Answer:** D. It prevents judges from defining criminal conduct through vague statutory terms

**Why:** Confusing the duty of precision with judicial interpretation overlooks why legality limits state coercion. The legislator alone holds democratic legitimacy to define offences; leaving vague texts for judges to clarify invites arbitrary criminalisation under the guise of statutory interpretation.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/the-requirement-of-lex-certa-binds-the-legislator-rather-than-the

### 4. In Spain a custom cannot create a criminal offence.

**Answer:** True

**Why:** **True**, and the contrast with private law is instructive. Custom is a source of the general legal order under Article 1.1 CC; in criminal law the requirement of *lex scripta* excludes it entirely, and the requirement is read further as a reserve of organic law wherever the penalty restricts fundamental rights.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/in-spain-a-custom-cannot-create-a-criminal-offence

### 5. Complete the requirements of the criminal statute.

**Answer:** That the statute must exist before the conduct is the requirement of lex **praevia**. That it must be written, and of statutory rank, is lex scripta. That it may not be extended by analogy against the accused is lex **stricta**. That it must describe the conduct precisely enough to guide a citizen is lex **certa**. Non bis in idem requires an identity of subject, of facts, and of **foundation**.

**Why:** The last blank is where the real litigation happens. Identity of subject and of facts is usually obvious; identity of **foundation** asks whether the two sanctions protect the same interest, and answering it decides whether an administrative fine and a criminal penalty for one episode may both stand.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/complete-the-requirements-of-the-criminal-statute

### 6. How many identities must coincide before the principle of non bis in idem prevents a second sanction?

**Answer:** 3

**Why:** **Three**: the same subject, the same facts, and the same foundation. The third is the one that is argued about, because it asks whether the two sanctions protect the same interest. Two sanctions on one person for one episode can both survive if, and only if, they are protecting genuinely different things.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/how-many-identities-must-coincide-before-the-principle-of-non-bis-in

### 7. The prohibition of analogy in criminal law bars any analogical reasoning whatever, including reasoning that favours the accused.

**Answer:** False

**Why:** **False.** The target of the prohibition is extension **against** the accused: punishing conduct the statute never described. The Code itself provides an expressly analogical mitigating circumstance, which shows that analogical reasoning as such is not banned. How far analogy in the accused's favour extends beyond such express provisions is genuinely disputed among Spanish writers.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/the-prohibition-of-analogy-in-criminal-law-bars-any-analogical

### 8. Arrange the checks a court makes under the principle of legality, in the order they arise.

**Answer:**

1. A written statute of the required rank described the conduct before it was done
2. The description covers this conduct without being extended by analogy
3. The statute itself fixes the penalty to be imposed
4. The penalty is imposed by the competent court in the process laid down
5. The sentence is served in the manner laid down by law and regulation

**Why:** Read downwards, the five checks are the four guarantees with the requirements of the statute folded into the first three. That is the useful way to hold them: the guarantees describe the stages at which legality bites, and the requirements describe the quality the statute must have for the first two stages to mean anything.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/arrange-the-checks-a-court-makes-under-the-principle-of-legality-in

### 9. Sort each defect by the requirement of the criminal statute that it violates.

**Answer:**

- Lex praevia: Past acts punished, Past penalty raised
- Lex stricta: Analogy to a horse, Analogy by purpose
- Lex certa: Vague social order, Vague good practice

**Why:** The middle column contains judicial defects and the outer two contain legislative ones, which is worth noticing. *Lex praevia* and *lex certa* are addressed to the legislator, and a court can do nothing to repair a vague statute except decline to apply it; *lex stricta* is addressed to the court, and no amount of legislative care prevents a judge from stretching a good provision.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/sort-each-defect-by-the-requirement-of-the-criminal-statute-that-it

### 10. Which are true of the requirement of lex certa?

A. The requirement binds the legislator and not only the judge who applies the provision
B. The legislator must describe the conduct precisely enough for a citizen to know what is forbidden
C. A provision may be as open as convenient, since the courts will supply its content case by case
D. A provision too vague to give guidance can be unconstitutional for that reason alone

**Answer:** A. The requirement binds the legislator and not only the judge who applies the provision; B. The legislator must describe the conduct precisely enough for a citizen to know what is forbidden; D. A provision too vague to give guidance can be unconstitutional for that reason alone

**Why:** The fourth describes exactly the practice the requirement forbids. If the content of an offence is settled by the courts after the fact, the citizen cannot know before acting what is prohibited, which returns you to the position that legality exists to escape, with the added disadvantage of looking lawful.

Page: https://tryals.app/practice/law-i/the-principle-of-legality/which-are-true-of-the-requirement-of-lex-certa