What is the difference between an ex post facto law and a bill of attainder?

Answer 1

Ex Post Facto literally means "After the fact". Putting it simply, it is a law passed after someone has committed some legal act until said law was passed, making it illegal. An ex post facto law is a law that retroactively punishes an act that would not have been punished before the enactment of a law. So basically, let's say that someone commits an act that is perfectly legal, then the legislature passes a law making the act illegal. One can not be retroactively prosecuted for the act that was committed while it was legal. Prohibition is a good example. Say a restraunteur was serving Alcoholic Beverages at his/her establishment. Then the legislature passes a law that outlaws alcohol. The restraunteur can not be punished for the sale of alcohol before the law was enacted, only for the sale of alcohol after the law was enacted.

"Bill of Attainder" means that you are prosecuted without a trial. Furthermore, there are three requirements for a "Bill of Attainder", there must be: (1) specification of the affected person(s); (2) punishment; and (3) lack of a judicial trial. 16B Am. Jur. 2D Constitutional Law § 716 (2009). In other words, the legislature can not pass a law which punishes something without a trial. The Bill of Attainder clause in the Constitution protects citizens against the legislature carrying out functions of the judicial branch. It protects you from being found guilty by legislative act as opposed to a court or jury of your peers.