Nullum Crimen Sine Lege

In one line

Nothing is a crime unless a law in force when it was done said so, and nothing may be punished more heavily than that law allowed.

In the wording a student can write in an exam: the principle of legality is expressed in two maxims, nullum crimen sine lege, no crime without a law, and nulla poena sine lege, no punishment without a law, and it has four consequences, namely that a criminal law may not operate retrospectively, that a court may not create an offence, that a court may not extend an offence by analogy to conduct the words do not cover, and that a penal provision must be construed strictly and any real ambiguity resolved in favour of the accused; in India the first two of these are guaranteed by article 20(1) of the Constitution.

The two maxims

Nullum crimen sine lege. No crime without a law. Conduct is not criminal unless a law in force at the time made it so.

Nulla poena sine lege. No punishment without a law. A person may not be punished except in the manner and to the extent the law provided when the act was done.

The full classical form adds nullum crimen sine lege praevia, scripta, stricta et certa: the law must be previous, written, strictly construed and certain. The last of those, certainty, is important enough to have a chapter of its own.

Article 20(1)

The text. No person shall be convicted of any offence except for violation of a law in force at the time of the commission of the act charged as an offence, nor be subjected to a penalty greater than that which might have been inflicted under the law in force at the time of the commission of the offence.

Two limbs, and they are distinct.

The first limb protects against conviction under a law made after the act. Conduct lawful when done cannot be made criminal afterwards.

The second limb protects against an increased penalty. Even where the conduct was already an offence, the punishment may not be raised retrospectively.

Three things the article does not do, and they are the marks.

It does not protect against a change of procedure. A person has no vested right in a form of procedure, so procedural amendments may be applied to pending cases. That is the distinction drawn in Module I's chapter on substantive and procedural criminal law.

It does not protect against a reduction of punishment. A person may take the benefit of a lighter penalty enacted afterwards, because the article is a protection and not a disability.

And it does not apply to preventive detention or to civil consequences. It applies to a conviction for an offence and to the penalty for it.