There are two branches to the Imperial Bureaucracy. Magisters Administrator keep the Empire running and are de facto rulers (in the Emperor's name) of the sub-divisions of the Empire. Magisters Judiciary are lawyers and counsels. The lower ranks are like circuit judges, doing the rounds of the provinces and overseeing justice. They have powers to deputise, arrest or subpoena anyone they choose (barring criminals and lunatics).
Junior bureaucrats begin as clerks, and upon reaching the highest level of clerk they may choose to follow the Administrator or Judiciary branch. Judiciary exams are harder and that branch is smaller. Each level is reached by study and passing exams (bribery and nepotism are technically illegal but practised).
The descriptions in brackets next to the titles given in the side-bar indicate rank the size of the region covered by each level of the Magisterial types. There is usually more than one Magister for each level. Grand Magisters are given ministerial posts governing the whole Empire and are expected to live in the royal court at Reflected Glory. Magisters of the Twelve Rivers are law lords and are responsible for setting new laws.
Official documents in the bureaucracy use "High Imperial", an older and more formal variant of the Imperial tongue ("Low Imperial" being the variant in common usage).
The grammar of High Imperial differs depending on whether one is addressing a superior or inferior. To further complicate things (and one of the reasons for the Empire's decline), an archaic rule states that a bureaucrat may not address directly anyone more than one level above or below them. This means that communication between the top and bottom of the hierarchy is slow, unwieldy and liable to error.
In breakaway provinces where Imperial-style bureaucratic meritocracy has been kept as a system of government this rule has been done away with (e.g. Magistracy of Nirhamsa). Official business is conducted in Low Imperial or Trade-tongue. Several layers of hierarchy have been stripped away and inter-level communication is much freer.