Incompatibilitas (Latin, 'incompatibility') was a principle instituted in the Kingdom of Poland (later, from 1569, in the Polish–Lithuanian Commonwealth), which forbade an individual to hold two or more official administrative positions.
The principle of incompatibilitas evolved in the 15th-16th centuries in response to a demand from middle and lesser nobility (Szlachta), and it was designed to curtail the sway of more powerful high nobility/aristocracy/plutocracy (the Magnates).
The specific acts of law that constituted the incompatibilitas rule were bans on holding: Commonwealth ministers were the equivalents of modern central-government officials.
Hetmans were also considered "ministers" but had no seat in the Senat.
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