- Joined
- Jul 13, 2017
I'm trying to remember the legal term for the idea that you can't be prosecuted for committing a crime if it wasn't actually a crime when you did it. "Grandfathered" maybe?
Ex post facto.
The actual legal concept in the US you are thinking of is the prohibition of ex post facto (lit. "out of the aftermath") laws. See US Constitution, Article 1, Sections 9-10.
It is unconstitutional for the government to punish somebody if the act was not codified as illegal at the precise moment it was committed.
In some countries, they can still do ex post facto bullshit. For example, the British Parliament follows the doctrine of "parliamentary supremacy." They can scream "I AM THE LAW!", criminalize something, and then retroactively apply the penalties to acts prior to them criminalizing it. The founding fathers thought that was ripe for abuse, so they made it so that neither the Federal government, or the states, could ever do it.