Short answers, pulled from the story.
Theodor Mommsen proposed that the era beginning with Diocletian marked a complete break from earlier republican traditions. He argued that imperial authority shifted from being embedded within existing institutions to becoming the state itself. His notes described this shift as a fundamental rupture where the old tripartite title of Augustus lost its magisterial nature.
Diocletian implemented specific political and military changes during his reign which defined the period historians once called the Dominate. He introduced genuflection into court ceremonies requiring subjects to bow before him rather than shake hands or kiss him like previous emperors. These reforms included the reintroduction of the universally current gold coin known as the Solidus by Constantine.
The word dominus initially denoted slave owners before becoming a new title for both the Emperor and a god. By the third century, addressing the Emperor as dominus began to gain ground across the empire. Coins from the reign of Aurelian expressed official power through the phrase domino et deo nato meaning born to be lord and god.
Ronald Syme significantly challenged the explanatory power of the Mommsenian model during the 1910s and 1930s. He placed more value on networks of people rather than strict legal frameworks when analyzing Roman politics. German historian Jochen Bleicken argued in 1978 that dividing imperial rule into Principate and Dominate lacked genuine constitutional transformation.
Markéta Melounová analyzed judicial trials concerning religious and political offences to test traditional historical divisions. Her research found little substantive difference between periods conventionally labelled as Principate and Dominate. Legal case studies demonstrate continuity in judicial processes across what was once considered a fundamental rupture.
The Oxford Classical Dictionary now regards dominate as a near-obsolete analytical term for modern scholarship. Since the start of the 20th century, scholars have increasingly rejected this view of a rupture around Diocletian. Historians now prefer broader views shaped by social and political sciences over strict constitutional frameworks.