congress may make no law making a previous legal act illegal retroactively
The Constitution of the United States forbids Congress and the states to pass any ex post facto law. In 1798 it was determined that this prohibition applies only to criminal laws and is not a general restriction on retroactive legislation.
Ex post facto law, law that retroactively makes criminal conduct that was not criminal when performed, increases the punishment for crimes already committed, or changes the rules of procedure in force at the time an alleged crime was committed in a way substantially disadvantageous to the accused.
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ex post facto law, law that retroactively makes criminal conduct that was not criminal when performed, increases the punishment for crimes already committed, or changes the rules of procedure in force at the time an
alleged crime was committed in a way substantially disadvantageous to the accused.
The
Constitution of the United States forbids Congress and the states to pass any ex post facto law. In 1798 it was determined that this prohibition applies only to criminal laws and is not a general restriction on retroactive legislation.
Implicit in the prohibition is the notion that individuals can be punished only in accordance with standards of conduct that they might have
ascertained before acting. The clause also serves, in conjunction with the prohibition of bills of
attainder, as a safeguard against the historic practice of passing laws to punish particular individuals because of their political beliefs. In 1867, in
Cummings v.
Missouri and
Ex parte Garland, the
United States Supreme Court condemned as both bills of attainder and ex post facto laws the passage of post-
American Civil War loyalty-test oaths, which were designed to keep Confederate sympathizers from practicing certain professions.
The policies
underlying ex post facto laws are recognized in most developed legal systems, reflected in the
civil law maxim
nulla poena sine lege (“no punishment without law”), a principle whose roots are embedded in
Roman law. In England
Parliament is not prohibited from passing ex post facto laws. However, following the
common-law tradition, judges have refused to interpret legislation retroactively unless Parliament has clearly expressed such an intention.