Aristotle, Nicomachean Ethics
H. Rackham, Ed.

Both are monarchies, but there is a very wide difference between them: a tyrant studies his own advantage, a king that of his subjects. For a monarch is not a king¹ if he does not possess independent resources, and is not better supplied with goods of every kind than his subjects; but a ruler so situated lacks nothing, and therefore will not study his own interests but those of his subjects. （A king who is not independent of his subjects will be merely a sort of titular king.²） Tyranny is the exact opposite in this respect, for the tyrant pursues his own good. The inferiority of Tyranny among the perversions is more evident than that of Timocracy among the constitutions, for the opposite of the best must be the worst. [3]

When a change of constitution takes place, Kingship passes into Tyranny, because Tyranny is the bad form of monarchy, so that a bad king becomes a tyrant. Aristocracy passes into Oligarchy owing to badness in the rulers, who do not distribute what the State has to offer according to desert, but give all or most of its benefits to themselves, and always assign the offices to the same persons, because they set supreme value upon riches; thus power is in the hands of a few bad men, instead of being in the hands of the best men. Timocracy passes into Democracy, there being an affinity between them, inasmuch as the ideal of Timocracy also is government by the mass of the citizens, and within the property qualification all are equal. Democracy is the least bad