The term "ex post facto" refers to what kind of law?

The term "ex post facto" refers specifically to laws that apply retroactively to make an act illegal after it has already been performed. This concept is rooted in the principle of fairness and justice, as applying such a law after the fact can punish individuals for actions that were legal at the time they were taken. The Constitution of the United States explicitly prohibits ex post facto laws under Article I, Section 9, for federal legislation, and Section 10 prohibits states from enacting such laws as well. This ensures that individuals cannot be retroactively penalized for actions they had no reason to believe were unlawful.

In contrast, laws that apply to future actions, provide exemptions, or are only applicable in emergencies do not fit the definition of ex post facto and reflect different legal principles. Recognizing the significance of this protection helps to understand how legal systems aim to safeguard individuals from arbitrary or unfair legal repercussions.