Ex post facto

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In Latin, ex post facto literally means from that which is done afterward. In English, we use it to mean after the fact. It’s primarily a legal term, and it can sound out of place in informal contexts, where after the fact or synonyms such as retroactive work just as well. Ex post facto is usually used as an adjective, but it also works as an adverb. Here are a few examples of the phrase in action in legal contexts:

The Swiss Supreme Court will intervene ex post facto only on restrictive grounds. [International Law Office]

They were hearings ex post facto, held to gather input on a proposal that is not a proposal at all, but rather the law of the District of Columbia. [Washington Post]

In an opinion by Walker, the majority found to be “without merit” the ex post facto claim, but only after citing United States v. Rodriguez. [Law.com]

And the phrase is occasionally used in non-legal contexts:

Later in the day, National Oceanic and Atmospheric Administration (NOAA) and Environmental Protection Agency (EPA) regulators … gave an ex post facto clean bill of health to the spill response’s heavy use of the chemical dispersant Corexit 9500. [World Socialist Web Site]

That sort of scenario was not the ex post facto invention of a Hollywood screenwriter. [Salon]