Division of labour is fundamental to Plato's political thought, and his views on this subject reveal both its strengths and its weaknesses. Since justice in the state is defined as "properly keeping one's own and doing one's own job" (IV, 434), it is essential that "one's own job" is properly defined and the "one man, one job" principle justified.
The topic of division of labour is introduced while explaining the origins of the state; Socrates lays down the minimum conditions for a community, which would at least require the skills of farming, building, weaving and a shoemaking (II, 369). Taking the obvious point that it is more efficient for one person to do each of these jobs, rather than for everyone to try all of them, Socrates draws the conclusion that "We have different natural aptitudes, which fit us for different jobs" (II, 370). While we are accustomed to seeing natural aptitudes as perhaps limiting the range of jobs a person may do (e.g. a weak person would not make a good blacksmith), Plato's view seems to be that these aptitudes are enough to determine the ideal profession for any person. This is in line with the Socratic vien line with the Socratic view of education, which is seen as a "drawing out" of what is already in a person, rather than adding skills and knowledge to a "blank sheet".
What is first presented as a purely practical argument has an ideological purpose. Plato, along with many thinkers of his time, saw politics as a skill (techne); a ruler is compared to a doctor or a ship's captain (I, 342), and even Thrasymachus employs the analogy of a ruler being like a shepherd (I, 343). However, according to Plato, this skill can not be learnt by anyone, but can only be the result of developing an aptitude which a person already possesses, in the same way that only a person who has a natural aptitude for weaving can become a good weaver. Thus, when the community grows to the point where it needs soldiers and governors, it is assumed that...