No statute is to have a retrospect beyond the time of its commencement.

Explanation

(English-origin maxim.) Statutes operate prospectively only — a law cannot reach back to punish or alter rights that were vested before its enactment.

Where this applies

• A state passes a law increasing penalties for drug possession and tries to apply the higher penalties to people convicted before the law was enacted, but the court blocks the retroactive application.
• A new tax statute is enacted in 2025 and the state tries to collect the new tax on income earned in 2024, but the court holds the statute cannot reach back before its effective date.
• A professional licensing board changes its requirements and revokes licenses of practitioners who qualified under the old rules, but the court rules the new standards cannot be applied retroactively to strip vested rights.

See also

• 2.3.1 Liberty is the natural power of doing whatever one pleases, except that which is restrained by law or force.