What is the fundamental principle underlying the concept of judicial review?

The fundamental principle underlying judicial review is the idea of the separation of powers and the concept of constitutional supremacy. The separation of powers, established by the U.S. Constitution, divides governmental authority among three distinct branches: the legislative (Congress), the executive (President), and the judicial (courts). Each branch has specific powers and responsibilities, designed to prevent any one branch from becoming too powerful. Judicial review is the power of the judiciary, particularly the Supreme Court, to examine laws and actions of the legislative and executive branches and determine whether they are constitutional.

Constitutional supremacy means that the Constitution is the highest law of the land. All other laws – federal, state, and local – must conform to it. If a law or action conflicts with the Constitution, it is considered invalid. Judicial review is the mechanism by which this principle of constitutional supremacy is enforced.

While the Constitution does not explicitly mention judicial review, it was established through the landmark Supreme Court case *Marbury v. Madison* (1803). In this case, the Court, under Chief Justice John Marshall, addressed the question of whether a law passed by Congress (the Judiciary Act of 1789) was constitutional. Marshall argued that it was the Court’s duty to interpret the Constitution and that when a law conflicts with the Constitution, the Constitution must prevail. The Court declared a portion of the Judiciary Act unconstitutional, effectively establishing the principle of judicial review.

Therefore, judicial review isn't about the courts creating law; it’s about ensuring that laws and actions made by other branches adhere to the pre-existing framework of the Constitution. If a law is found unconstitutional, it doesn't mean the Court is changing the Constitution itself, but rather that the law is deemed to be beyond the scope of what the Constitution allows. For example, if Congress passes a law restricting freedom of speech beyond what the First Amendment permits, the Supreme Court can declare that law unconstitutional, nullifying its effect. This process maintains the balance of power and upholds the Constitution as the supreme law of the land.