In countries with unwritten or uncodified constitutions, such as the United Kingdom, conventions and customs are essential. Because there is no single document that outlines all governmental procedures, these long-standing practices and political norms fill the gaps, providing the necessary rules for the operation of political institutions and the conduct of public officials.

James Wilford Garner (often misspelled as Garnet in some texts) is famous for his definition of the state as a community of persons, more or less numerous, permanently occupying a definite portion of territory, independently of external control, and possessing an organized government to which the great body of inhabitants render habitual obedience. These four elements—population, territory, government, and sovereignty—remain the standard academic definition.

A constitution is classified as rigid when it requires a complex, difficult, or special amendment process to alter its provisions. Unlike flexible constitutions that can be changed through ordinary legislative acts, rigid constitutions often mandate supermajorities, ratification by sub-national units, or other procedural hurdles to ensure that fundamental laws are not easily modified by transient political majorities.

Sovereignty is the supreme authority of a state to govern itself and its territory without external interference. According to classical political theory, sovereignty is an essential, indivisible, and permanent element of any state, regardless of its specific form of government. Whether a state is a democracy, a dictatorship, or a monarchy, it must possess sovereignty to be recognized as a legitimate political entity within the international system.

While unwritten constitutions rely heavily on conventions, written constitutions also incorporate customs and conventions to fill gaps in formal legal text. These practices provide essential guidance for governance, ensuring that the formal document remains functional and adaptable to changing political circumstances without requiring constant formal amendments.

Erich Kaufmann, a German legal scholar, viewed the state through a power-centric lens. He argued that the state's fundamental nature is defined by its capacity to develop, increase, and project power. This perspective aligns with the tradition of 'Machtpolitik' (power politics), where the state's survival and influence are contingent upon its ability to assert its authority and strength in both domestic and international arenas.

According to the Montevideo Convention, the four essential elements of a state are a permanent population, a defined territory, a government, and the capacity to enter into relations with other states, which is fundamentally rooted in the possession of sovereignty. Sovereignty is the supreme authority that allows a state to exercise control over its territory and population without external interference.

According to the Montevideo Convention and standard political theory, a state must possess four essential elements: a permanent population, a defined territory, a functioning government, and the capacity to enter into relations with other states, which is derived from sovereignty.

In a federal structure, states are sovereign or semi-sovereign entities that derive their authority from the constitution, not from the central government. They possess their own legislative, executive, and judicial branches. Consequently, they are distinct from local government units, which are typically created by state or central legislation and function as subordinate administrative entities rather than as autonomous federal components.

In international law, while states possess sovereign rights, the expropriation or nationalization of foreign-owned property is generally subject to the requirement of 'prompt, adequate, and effective' compensation. This principle protects the rights of foreign investors and maintains stability in international economic relations, distinguishing it from arbitrary seizure.