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In law and government, de jure (/ , -, -/ day JOOR-ee, dee -, YOOR-ee; Latin: dē iūre pronounced [deː ˈjuːrɛ], "by law") describes practices that are legally recognized, regardless of whether the practice exists in reality. In contrast, de facto ("in fact") describes situations that exist in reality, even if not legally recognized.
Between 1805 and 1914, the ruling dynasty of Egypt ruled as de jure viceroys of the Ottoman Empire, but acted as de facto independent rulers who maintained a polite fiction of Ottoman suzerainty. However, starting from around 1882, the rulers had only de jure rule over Egypt, as it had by then become a British puppet state. Thus, Egypt was by Ottoman law de jure a province of the Ottoman Empire, but de facto was part of the British Empire.
In U.S. law, particularly after Brown v. Board of Education (1954), the difference between de facto segregation (segregation that existed because of the voluntary associations and neighborhoods) and de jure segregation (segregation that existed because of local laws that mandated the segregation) became important distinctions for court-mandated remedial purposes.
In a hypothetical situation, a king or emperor could be the de jure head of state. However, if they are unfit to lead the country, the prime minister or chancellor would assumedly become the practical, or de facto leader, while the king remains the de jure leader.