ex post facto

American  

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

adverb

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

---

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

---

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.”

---

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.”

---

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

No relevant precedent existed, and given the unique crimes the Nazi hierarchy had committed, it would require ex post facto laws to prosecute them.

From Salon • May 18, 2026

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

So many shows rely on studio interviews or guests recapping their adventures ex post facto — the equivalent of Aunt Jane prattling on about her trip to Tuscany over the phone.

From Washington Post • Dec. 10, 2020

Because Wayna Qhapaq had not actually married Washkar’s mother—the union was properly incestuous but not properly legitimate—the new Inka demanded that his mother participate ex post facto in a wedding ceremony with his father’s mummy.

From "1491" by Charles C. Mann