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What Does "Ex Tunc" Mean?

Jessica Ellis
Updated May 16, 2024
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Ex tunc is a legal phrase that means “from the outset.” It is generally used in law to describe situations where a law or ruling applies to past events, rather than events from the present moving forward. An ex tunc ruling or law might have a retroactive effect in certain cases, meaning that events prior to the existence of the ruling or law might be judged in accordance with it.

Commonly, ex tunc issues are closely involved with contract law. In any type of contract, whether a business agreement, marriage, or lease, an ex tunc ruling might hold that the contract was valid, invalid, or altered dating from the beginning of the contract, rather than the date of the ruling. In marriage, for example, a divorce dissolves the union from the ruling date onward, while an annulment decrees that the marriage was never valid. Annulment, therefore, is an ex tunc ruling, while divorce is known as an ex nunc, or “from now on” ruling.

Determining whether a legal decision is effective from the outset or may be vital to meting out damages in certain trials. With an invalid lease, for instance, a landlord might be ordered to pay back rent to the tenant if the lease is declared invalid ex tunc. If it is declared ex nunc, however, the tenant may be out any rent paid, since the invalidation is only effective from the date of the ruling.

"From the outset" rulings and judgments are also sometimes applied to patent or intellectual property decrees. If a person patents a design, then makes a significant change to the design, he or she may have to apply for a patent alteration. Under some systems of patent law, the change might be declared ex tunc, meaning that the patent for the altered design legally existed from the outset. Though this may sound somewhat illogical, it helps simplify the patent process and can help reduce patent disputes based on imitation, or slightly altered products.

An ex tunc law is a fairly rare occurrence, since the retroactive effects can cause serious legal complications. If people have been prosecuted under a law declared invalid ex tunc, there may be confusion of the legality of all previous trials and the necessity for reparations made to those tried and convicted of a law now considered invalid from the outset. For this reason, many laws that repeal or alter earlier statutes take effect from the date of the ruling onward.

MyLawQuestions is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Jessica Ellis
By Jessica Ellis , Writer
With a B.A. in theater from UCLA and a graduate degree in screenwriting from the American Film Institute, Jessica Ellis brings a unique perspective to her work as a writer for MyLawQuestions. While passionate about drama and film, Jessica enjoys learning and writing about a wide range of topics, creating content that is both informative and engaging for readers.

Discussion Comments

By JimmyT — On Sep 11, 2011

@stl156 - I have never been involved with a probate situation, but I know the courts are responsible for making sure a will is executed legally.

I don't know how the system works if a case like that would be decided case by case with the local judge, or if there is a protocol for those situations. It's a good question, though, and I'm sure it has happened.

By stl156 — On Sep 10, 2011

It seems like most of the rulings that fall under ex tunc are things that involve some document being signed, not so much criminal laws.

I was wondering what would happen with probate law. If you made your will and then the law changed and there was some sort of amendment concerning estate laws, would your will follow the laws at the time you made it or the time it came into effect? What if you were never aware that the new law was put in place?

Jessica Ellis

Jessica Ellis


With a B.A. in theater from UCLA and a graduate degree in screenwriting from the American Film Institute, Jessica Ellis...
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