Why did written constitutions come to be treated as higher law?

Written constitutions are treated as "higher law" because they are viewed as the sovereign embodiment of the people's will, taking precedence over the actions of any specific government branch or legislative majority. This status emerged from several key historical and theoretical developments:12

• Natural Rights Doctrine: Enlightenment thinkers, such as John Locke, argued that individuals possess inalienable rights that governments do not create and therefore cannot take away. Written constitutions were designed to codify these rights and limit governmental power to ensure their protection.12
• Sovereignty of the People: As the concept of the "people as a whole" replaced the monarch as the source of sovereignty, the constitution—as the written expression of that collective will—became supreme over any subdivision of the people, including the legislature.2
• Entrenchment: By establishing formal, difficult amendment procedures (such as supermajorities), written constitutions became "rigid," preventing them from being altered by the same simple processes used for ordinary statutes.312
• Institutional Control: This higher status enables judicial review, allowing independent courts to ensure that ordinary legislation conforms to constitutional principles, thereby preventing government branches from acting as "judges in their own cause".412