An oligarchy, in the sense which we have assigned to the word, could only exist where there was an inferior body which felt itself aggrieved by being excluded from the political rights which were reserved to the privileged few. Such a feeling of discontent might be roused by the rapacity or insolence of the dominant order, as we shall find to have happened at Athens, and as was the case at Mytilene, where some members of the ruling house of the Penthilids went about with clubs, committing outrages like those which Nero practised for a short time in the streets of Rome. But, without any such provocation, disaffection might arise from the cause which we shall see producing a revolution at Corinth, where the aristocracy was originally established on a basis too narrow to be durable: as Aristotle relates of the Basilids at Erythræ, that, though they exercised their power well, they could not retain it, because the people would no longer endure that it should be lodged in so few hands. In general however it was a gradual, inevitable change in the relative position of the higher and lower orders, which converted the aristocracy into an oligarchical faction, and awakened an opposition which usually ended in its overthrow. The precautions which were used by the ruling class, when it began to perceive its danger, were of various kinds, and it was more frequently found necessary to widen the oligarchy itself, by the admission of new families, and to change the principle of its constitution by substituting wealth for birth as the qualification of its members. The form of government in which the possession of a certain amount of property was the condition of all, or at least of the highest, political privileges, was sometimes called a timocracy, and its character varied according to the standard adopted. When this was high, and especially if it was fixed in the produce of land, the constitution differed little in effect from the aristocratical oligarchy, except as it opened a prospect to those who were excluded of raising themselves to a higher rank. But, when the standard was placed within reach of the middling class, the form of government was commonly termed a polity, and was considered as one of the best tempered and most durable modifications of democracy. The first stage however often afforded the means of an easy transition to the second, or might be reduced to it by a change in the value of the standard.