<P> Some common - law jurisdictions do not permit retroactive criminal legislation , though new precedent generally applies to events that occurred before the judicial decision . Ex post facto laws are expressly forbidden by the United States Constitution in Article 1 , Section 9 , Clause 3 ( with respect to federal laws ) and Article 1 , Section 10 ( with respect to state laws ) . In some nations that follow the Westminster system of government , such as the United Kingdom , ex post facto laws are technically possible , because the doctrine of parliamentary supremacy allows Parliament to pass any law it wishes . In a nation with an entrenched bill of rights or a written constitution , ex post facto legislation may be prohibited . </P>
<P> Some common - law jurisdictions do not permit retroactive criminal legislation , though new precedent generally applies to events that occurred before the judicial decision . Ex post facto laws are expressly forbidden by the United States Constitution in Article 1 , Section 9 , Clause 3 ( with respect to federal laws ) and Article 1 , Section 10 ( with respect to state laws ) . In some nations that follow the Westminster system of government , such as the United Kingdom , ex post facto laws are technically possible , because the doctrine of parliamentary supremacy allows Parliament to pass any law it wishes . In a nation with an entrenched bill of rights or a written constitution , ex post facto legislation may be prohibited . </P>
where is the ex post facto law in the constitution
where is the ex post facto law in the constitution
Article 1 , Section 9 , Clause 3 ( with respect to federal laws ) and Article 1 , Section 10 ( with respect to state laws )
Article 1 , Section 9 , Clause 3 ( with respect to federal laws ) and Article 1 , Section 10 ( with respect to state laws )