Aristotle, Politics

¹Almost all the other subjects which we intended to treat [20] have now been discussed. There must follow the consideration of the questions, what are the number and the nature of the causes that give rise to revolutions in constitutions, and what are the causes that destroy each form of constitution, and out of what forms into what forms do they usually change, and again what are the safeguards of constitutions in general and of each form in particular, and what are the means by which the safeguarding of each may best be put into effect.²

And we must first assume the starting-point, that many forms of constitution have come into existence with everybody agreeing as to what is just, that is proportionate equality, but failing to attain it （as has also been said before）. Thus democracy arose from men's thinking that if they are equal in any respect they are equal absolutely （for they suppose that because they are all alike free they are equal absolutely）, oligarchy arose from their assuming that if they are unequal as regards some one thing they are unequal wholly （for being unequal in property they assume that they are unequal absolutely）; and then the democrats claim as being equal to participate in all things in equal shares, while the oligarchs as being unequal seek to have a larger share, for a larger share is unequal. All these forms of constitution then have some element of justice, but from an absolute point of view they are erroneous; and owing to this cause, when each of the two parties has not got the share in the constitution which accords with the fundamental assumption that they happen to entertain, faction ensues. And of all men those who excel in virtue would most justifiably stir up faction, though they are least given to doing so;