ex post facto

American  

[eks pohst fak-toh] / ˈɛks ˌpoʊst ˈfæk toʊ /

adverb

1. from or by subsequent action; retroactively; subsequently; retrospectively.

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adjective

1. having retroactive force; made or done subsequently.

   an ex post facto law.

ex post facto British  

/ ɛks pəʊst ˈfæktəʊ /

adjective

1. having retrospective effect

   an ex post facto law

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ex post facto ¹ Cultural  

1. An explanation or regulation concocted after the event, sometimes misleading or unjust: “Your ex post facto defense won't stand up in court.” (See ex post facto law.) From Latin, meaning “after the deed.”

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ex post facto ² Cultural  

1. A descriptive term for an explanation or a law that is made up after an event and then applied to it: “The chairman's description of his plan sounds like an ex post facto attempt to justify an impulsive action.” Ex post facto is Latin for “from after the deed.”

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Etymology

Origin of ex post facto

First recorded in 1625–35; from Latin: “from a thing done afterward, from what is done afterward”

Example Sentences

The effects have been so strong that the Fed, in a heroic feat of ex post facto rationalization, has begun to think of asset prices as another transmission mechanism for its balance-sheet policy instrument.

From The Wall Street Journal • Apr. 21, 2026

“This is a violation of the ex post facto clause of the constitution,” said Neama Rahmani, president of West Coast Trial Lawyers.

From Washington Times • Feb. 10, 2023

As for the claim of ex post facto justice, Robert Jackson — the American prosecutor who believed aggression enabled all the other war crimes that followed — summed up the charge:

From Salon • Jan. 7, 2023

Because genocide became an official crime only after the Nuremberg trials, Germany decided in 1949 that charging former Nazis with this crime would amount to ex post facto law.

From Washington Post • Oct. 6, 2021

There is reason to believe that recollection was an ex post facto elaboration; those on the scene recall a sensation more suggestive of relief and euphoria in the air.

From "Big Science" by Michael Hiltzik