Principle of rulership Aristotle believes that the existence and well-being of any system requires the presence of a ruling element: “Whenever a thing is established out of a number of things and becomes a single common thing, there always appears in it a ruler and ruled …. This [relation] is present in living things, but it derives from all of nature” (1254a28–32). Just as an animal or plant can survive and flourish only if its soul rules over its body (Pol. I.5.1254a34–6, De Anima I.5.410b10–15; compare Plato Phaedo 79e-80a), a human community can possess the necessary order only if it has a ruling element which is in a position of authority, just as an army can possess order only if it has a commander in control. Although Aristotle follows Plato in accepting this principle, he rejects Plato's further claim that a single science of ruling is appropriate for all (see Plato Statesman 258e-259c. For Aristotle different forms of rule are required for different systems: e.g., political rule for citizens and despotic rule for slaves. The imposition of an inappropriate form of rule results in disorder and injustice. This point becomes clearer in the light of the following corollary of the principle of rulership.