  The best human life is ruled by knowledge and especially knowledge of what goodness is and of what is good for human beings. So, too, is  the best city. For Plato, philosophers make the ideal rulers for two  main reasons. First, they know what is good. Second, they do not want to rule (esp. 520e–521b). The problem with existing cities is  correspondingly twofold. They are ruled by people who are ignorant of what is good, and they suffer from strife among citizens all of whom  want to rule. These flaws are connected: the ignorant are  marked by their desire for the wrong objects, such as honor and  money, and this desire is what leads them to seek political power.  All existing regimes, whether ruled by one, a few, or many,  show these defects. So in the Republic Socrates does not  distinguish between good and bad forms of these three kinds of  regime, as the Stranger does in the Plato’s Statesman  (301a–303b, cf. Aristotle, Politics III 7).