Skip to main content

Retroactivity of Legislation


A characteristic of arbitrary government is that the state can alter retroactively the legal status of acts already done. Therefore, proposals to prohibit various types of retroactive legislation encountered the opposition of those delegates to the constitutional convention of 1787 who believed such laws were "void of themselves" and that a formal prohibition would "proclaim that we are ignorant of the first principles of legislation." There are, nevertheless, three such prohibitions in the Constitution: Congress may not pass ex post facto laws and the states may not pass ex post facto laws or laws impairing the obligation of contracts.

There are sound historical reasons for supposing that the Framers meant to proscribe both criminal and civil legislation with retrospective application. But john dickinson had warned the convention that william blackstone's commentaries treated "ex post facto" as a technical term applying only to criminal law. In calder v. bull (1798), the Supreme Court relied on Blackstone's authority to confine the constitutional prohibition to criminal laws.

The contract clause ultimately proved a mere parchment barrier to retroactive legislation. It does not apply to the federal government and the courts have so interpreted it as to make it a weak defense against retroactive state laws.

Dennis J. Mahoney

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Retroactivity of Legislation." Encyclopedia of the American Constitution. . 20 Jan. 2019 <>.

"Retroactivity of Legislation." Encyclopedia of the American Constitution. . (January 20, 2019).

"Retroactivity of Legislation." Encyclopedia of the American Constitution. . Retrieved January 20, 2019 from

Learn more about citation styles

Citation styles gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, cannot guarantee each citation it generates. Therefore, it’s best to use citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.