State Laws

What is an ex post facto law?

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2017-01-25 12:42:35

An ex post facto law is one that is made retroactive to punish

an act that wasn't illegal at the time it was committed. For

example, if I didn't wear my seatbelt and wearing one wasn't a law,

but it became a law the next day, I couldn't get in trouble for it

because the "crime" was committed before it was against the


Article I of the US Constitution specifically says this cannot

be done. Laws that don't involve penalties can reference dates in

the past to allow an income tax break or permit eligibility for a

program based on past actions (such as fighting in a war).

The reason the Constitution prevents Congress (and the states)

from writing ex post facto laws is to protect the population and

other entities from government abuse.

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