In The Republic, Plato hypothesizes the formation of the ideal city, the kallipolis, as a way to embody the philosophical definition of perfect justice. In the just city, one is most likely to see the execution of perfect justice, and so the composition of this city will be the best indicator of justice as an idea. For Plato, justice had a simple definition (with a much more complicated rationalization): justice is each person in the city doing only the work to which they are best suited:
“Then, it turns out that this doing one’s own work – provided that it comes to be in a certain way – is justice.” (433b)
The argument that justice is each doing one’s own work transitions naturally into Plato’s (speaking through Socrates) next one, that the kallipolis should be ruled by philosopher-kings. If each person in the city-state is only best suited to one kind of work, if they want to carry out that work perfectly, then only a very select few people will actually possess the aptitude...
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