The Complete Aristotle (eng.)

by the people, although they may be required to have
a high qualification, or to be members of a political club; or,
again, where the law-courts are composed of persons outside the
government, the oligarchs flatter the people in order to obtain a
decision in their own favor, and so they change the constitution;
this happened at Heraclea in Pontus. Again, oligarchies change
whenever any attempt is made to narrow them; for then those who
desire equal rights are compelled to call in the people. Changes in
the oligarchy also occur when the oligarchs waste their private
property by extravagant living; for then they want to innovate, and
either try to make themselves tyrants, or install some one else in
the tyranny, as Hipparinus did Dionysius at Syracuse, and as at
Amphipolis a man named Cleotimus introduced Chalcidian colonists,
and when they arrived, stirred them up against the rich. For a like
reason in Aegina the person who carried on the negotiation with
Chares endeavored to revolutionize the state. Sometimes a party
among the oligarchs try directly to create a political change;
sometimes they rob the treasury, and then either the thieves or, as
happened at Apollonia in Pontus, those who resist them in their
thieving quarrel with the rulers. But an oligarchy which is at
unity with itself is not easily destroyed from within; of this we
may see an example at Pharsalus, for there, although the rulers are
few in number, they govern a large city, because they have a good
understanding among themselves.
    Oligarchies, again, are overthrown when another oligarchy is
created within the original one, that is to say, when the whole
governing body is small and yet they do not all share in the
highest offices. Thus at Elis the governing body was a small
senate; and very few ever found their way into it, because the
senators were only ninety in number, and were elected for life and
out of certain families in a manner similar to the Lacedaemonian
elders. Oligarchy is liable to revolutions alike in war and in
peace; in war because, not being able to trust the people, the
oligarchs are compelled to hire mercenaries, and the general who is
in command of them often ends in becoming a tyrant, as Timophanes
did at Corinth; or if there are more generals than one they make
themselves into a company of tyrants. Sometimes the oligarchs,
fearing this danger, give the people a share in the government
because their services are necessary to them. And in time of peace,
from mutual distrust, the two parties hand over the defense of the
state to the army and to an arbiter between the two factions, who
often ends the master of both. This happened at Larissa when Simos
the Aleuad had the government, and at Abydos in the days of
Iphiades and the political clubs. Revolutions also arise out of
marriages or lawsuits which lead to the overthrow of one party
among the oligarchs by another. Of quarrels about marriages I have
already mentioned some instances; another occurred at Eretria,
where Diagoras overturned the oligarchy of the knights because he
had been wronged about a marriage. A revolution at Heraclea, and
another at Thebes, both arose out of decisions of law-courts upon a
charge of adultery; in both cases the punishment was just, but
executed in the spirit of party, at Heraclea upon Eurytion, and at
Thebes upon Archias; for their enemies were jealous of them and so
had them pilloried in the agora. Many oligarchies have been
destroyed by some members of the ruling class taking offense at
their excessive despotism; for example, the oligarchy at Cnidus and
at Chios.
    Changes of constitutional governments, and also of oligarchies
which limit the office of counselor, judge, or other magistrate to
persons having a certain money qualification, often occur by
accident. The qualification may have been originally fixed
according to the circumstances of the time, in such a manner as to
include in an oligarchy a few only, or in a constitutional
government the middle class. But after a time of prosperity,
whether arising from peace or some other good fortune, the same
property becomes many times as valuable, and then everybody
participates in every office; this happens sometimes gradually and
insensibly, and sometimes quickly. These are the causes of changes
and revolutions in oligarchies.
    We must remark generally both of democracies and oligarchies,
that they sometimes change, not into the opposite forms of
government, but only into another variety of the