It would seem that all the possible solutions had been proposed, and that any others were inconceivable. The principles are one, many, infinite, or even do not exist; everything is in motion, everything is motionless; everything depends on the ordering intelligence of Mind, everything is derived from a mechanical movement. Thus it is possible to proceed in the list of the antithesis.
Let us remember, above all, the slow but inevitable crisis of the aristocracy, which went hand in hand with the always increasing power of the demos, of the people. Theses factors must also be kept in mind: the affluence in the cities, especially Athens; of an increasing number of metics, the widening of opportunities for commerce that surpassed the limiting restrictions of individual cities bringing each of them in contact with a much wider world, and the widening of experience and knowledge of the voyagers who brought to the fore the inevitable comparison of usages, customs, and laws in relation to wholly different usages, customs, and laws. All these elements must have constituted the first premise of relativism, causing the conviction that what was eternally stable and valid was instead lacking value in other circumstances and environments.
[In V in. BC,] the Sophists completely welcomed these attitudes of this period of turmoil in which they lived. And this explains why they achieved such a great success especially among the young. They answered to the real needs of the moment, they spoke to the young who were no longer satisfied with traditional values that their elders proposed nor with the manner in which they proposed them, and they gave the young the new language for which they were waiting.
Giovanni Reale – History of Ancient Philosophy