Constitutional Law

Legislative Branch

What does the Constitution say about ex post facto laws?

Article I, Section 10 prohibits Congress from passing ex post facto laws, which essentially are laws that have a retroactive and detrimental impact on individuals. Ex post facto laws are those which make conduct a crime even if the conduct was legal when originally committed. The U.S. Supreme Court explained the types of ex post facto laws in Calder v. Bull (1798):

I will state what laws I consider ex post facto laws, within the words and the intent of the prohibition. 1st. Every law that makes an action, done before the passing of the law, and which was innocent when done, criminal; and punishes such action. 2nd. Every law that aggravates a crime, or makes it greater than it was, when committed. 3rd. Every law that changes the punishment, and inflicts a greater punishment, than the law annexed to the crime, when committed. 4th. Every law that alters the legal rules of evidence, and receives less, or different, testimony, than the law required at the time of the commission of the offence, in order to convict the offender. All these, and similar laws, are manifestly unjust and oppressive.


This is a web preview of the "The Handy Law Answer Book" app. Many features only work on your mobile device. If you like what you see, we hope you will consider buying. Get the App