Which constitutional principle allows courts to determine the constitutionality of laws?

Judicial review is the constitutional principle that enables courts to evaluate the constitutionality of laws and government actions. This power was established in the landmark case of Marbury v. Madison in 1803, which set the precedent that it is the judiciary's role to interpret the law and ensure that legislative and executive actions comply with the Constitution.

Through judicial review, courts can strike down laws that are found to be in violation of constitutional provisions, thus ensuring that no law or governmental action can supersede constitutional rights and principles. This principle is foundational in maintaining the rule of law and protecting individual rights within a system of government.

The other principles mentioned, while integral to the structure of government, do not directly pertain to the function of courts in assessing the legality of laws. Separation of powers delineates the distinct roles of the legislative, executive, and judicial branches, checks and balances reinforce the system by allowing each branch to limit the powers of the others, and due process ensures fair treatment through the normal judicial system. However, none of these principles grant the authority to interpret the Constitution and assess the constitutionality of laws as judicial review does.