The following description of the sophists is taken from Frank Thilly, A History of Philosophy, 1914.
The new movement was represented by the Sophists. The term Sophist originally meant a wise and skilful man, but in the time we are describing it came to be applied to the professional teachers who traveled about, giving instruction for pay in the art of thinking and speaking, and preparing young men for political life. [The name gradually became a term of reproach, partly because the Sophists took pay, partly owing to the radicalism of some of the later Sophists, which scandalized the conservative element.]
To this task they devoted themselves with feverish zeal. “If you associate with me,” Protagoras is reported to have said to a young man, “on the very day you will return a better man than you came.” And when Socrates asks how he is going to bring this about, he answers: “If he comes to me, he will learn that which he comes to learn. And this is prudence in affairs, private as well as public; he will learn to order his house in the best manner, and he will be able to speak and act for the best in the affairs of the State." [Plato’s Protagoras.] In order to fit himself for a career, it was necessary for the young man to perfect himself in dialectics, grammar, rhetoric, and oratory. Such subjects the Sophists began to study with a practical end in view, and thus broke the soil for new fields of investigation. They also turned their attention to moral and political questions, and so gave the impetus to a more systematic and thorough treatment of ethics and the theory of the State. As the moral earnestness of the times declined, and the desire to succeed at all hazards intensified, some of the later Sophists, in their anxiety to make their pupils efficient, often went to extremes; it became the object of instruction to teach them how to overcome an opponent in debate by fair means or foul, to make the worse appear the better cause, to confuse him with all sorts of logical fallacies, and to render him ridiculous in the eyes of the chuckling public.
The critical spirit of the age, which had, in a large measure, been fostered by philosophy, began to react upon philosophy itself and led to a temporary depreciation of metaphysical speculation. Thought weighs itself in the balance and finds itself wanting; philosophy digs its own grave. No two philosophers, so it is argued, seem to agree in their answers to the question of the essence of reality. One makes it water, another air, another fire, another earth, and yet another all of them together; one declares change to be impossible, another says there is nothing but change. Now, if there is no change, there can be no knowledge: we cannot predicate anything of anything, for how can the one be the many? If everything changes, there can be no knowledge either; for where nothing persists, how can we predicate anything of anything? And if we can know things, only so far as they affect our senses, as some hold, again we cannot know, for then the nature of things eludes our grasp. The upshot of it all is, we cannot solve the riddle of the universe. The truth begins to dawn on the Sophist that the mind of man is an important factor in the process of knowing. Thinkers before him had assumed the competence of human reason to attain truth; with all their critical acumen they had forgotten to criticise the intellect itself. The Sophist now turns the light on the knowing subject and concludes that knowledge depends upon the particular knower, that what seems true to him is true for him, that there is no objective truth, but only subjective opinion. "Man is the measure of all things," so Protagoras taught. That is, the individual is a law unto himself in matters of knowledge. And from this theoretical skepticism, the step is not far to ethical skepticism, to the view that man is a law unto himself in matters of conduct. If knowledge is impossible, then knowledge of right and wrong is impossible, there is no universal right and wrong: conscience is a mere subjective affair. These consequences were not drawn by the older Sophists, by men like Protagoras (born about 490 B.C.) and Gorgias, but they were drawn by some of the younger radical set, by Polus, Thrasymachus, Callicles, and Euthydemus, who are spokesmen in Plato’s Dialogues. Morality to them is a mere convention; it represents the will of those who have the power to enforce their demands on their fellows. The rules of morals are contrary to " nature." According to some, laws were made by the weak, the majority, in order to restrain the strong, the " best," to hinder the fittest from getting their due: the laws, therefore, violate the principle of natural justice. Natural right is the right of the stronger. According to others, the laws are a species of class legislation; they are made by the few, the strong, the privileged, in order to protect their own interests. That is, it is to the advantage of the overman that others obey the laws so that he can the more profitably break them.
“The makers of the laws,” says Callicles in the Platonic dialogue Gorgias, “are the majority who are weak; and they make laws and distribute praises and censures with a view to themselves and their own interests; and they terrify the stronger sort of men, and those who are able to get the better of them, in order that they may not get the better of them; and they say that dishonesty is shameful and unjust; meaning by the word injustice the desire of a man to have more than his neighbors; for knowing their own inferiority, I suspect that they are too glad of equality. And therefore the endeavor to have more than the many, is conventionally said to be shameful and unjust, and is called injustice, whereas nature herself intimates that it is just for the better to have more than the worse, the more powerful than the weaker; and in many ways she shows, among men as well as among animals, and indeed among whole cities and races, that justice consists in the superior ruling over and having more than the inferior. For on what principle of justice did Xerxes invade Hellas, or his father the Scythians? (not to speak of numberless other examples). Nay, but these are the men who act according to nature; yes, by heaven, and according to the law of nature: not, perhaps, according to that artificial law, which we invent and impose upon our fellows, of whom we take the best and the strongest from their youth upwards, and tame them like young lions, — charming them with the sound of the voice, and saying to them, that with equality they must be content, and that the equal is the honorable and the just. But if there were a man who had sufficient force, he would shake off and break through, and escape from all this; he would trample underfoot all our formulas and spells and charms and all our laws which are against nature: the slave would rise in rebellion and be lord over us, and the light of natural justice would shine forth.”
Thrasymachus talks in the same strain in the Republic:
“The just is always a loser in comparison with the unjust. First of all, in private contracts: wherever the unjust is the partner of the just you will find that when the partnership is dissolved, the unjust man has always more and the just less. Secondly, in their dealings with the State: when there is an income-tax, the just man will pay more and the unjust less on the same amount of income; and when there is anything to be received the one gains nothing and the other much. Observe also what happens when they take an office; there is the just man neglecting his affairs and perhaps suffering other losses, and getting nothing out of the public, because he is just; moreover he is hated by his friends and acquaintances for refusing to serve them in unlawful ways. But all this is reversed in the ease of the unjust man. I am speaking as before of injustice on the large scale in which the advantage of the unjust is most apparent; and my meaning will be most clearly seen if we turn to that highest form of injustice in which the criminal is the happiest of men, and the sufferers or those who refuse to do injustice are the most miserable, — that is to say tyranny, which by fraud and force takes away the property of others, not little by little but wholesale; comprehending in one, things sacred as well as profane, private and public; for which acts of wrong, if he were detected perpetrating any of them singly, he would be punished and incur great disgrace, — they who do such wrong in particular cases are called robbers of temples, and man-stealers and burglars and swindlers and thieves. But when a man besides taking away the money of the citizens has made slaves of them, then, instead of these names of reproach, he is termed happy and blessed, not only by the citizens, but by all who have heard of the consummation of injustice. For mankind censure injustice, fearing that they may be the victims of it, and not because they shrink from committing it. And thus, as I have shown, Socrates, injustice, when on a sufficient scale, has more strength and freedom and mastery than justice; and, as I said at first, justice is the interest of the stronger, whereas injustice is a man’s own profit and interest.” [Jowett’s translation of Plato’s Dialogues.]
Significance of Sophistry
Owing to the hostile criticisms of Plato and Aristotle, as well as to the nihilistic teachings of some of the younger Sophists, the importance of the Sophistic movement in the history of thought was long misjudged. It is only since Hegel and Grote attempted to give a fairer estimate of these thinkers that justice has been done them. There was good and there was evil in their teachings. Reflection and criticism are indispensable to sounder conceptions in philosophy, religion, morals, politics, and in all fields of human endeavor. The appeal to reason was commendable in itself, but the fault lay in the inability of Sophistry to use the instrument of reason in anything like a constructive way. The Sophists brought philosophy down from heaven to the dwellings of men, as Cicero said, and turned the attention from external nature to man himself; with them the proper study of mankind was man. But they failed to recognize the universal element in man; they did not see the forest for the trees, they did not see man for men. They exaggerated the differences in human judgments and ignored the agreements. They laid too much stress on the illusion of the senses. They emphasized the accidental, subjective, and purely personal elements in human knowledge and conduct, and failed to do justice to the objective element, the principles which are accepted by all.
Nevertheless, their criticisms of knowledge made necessary a profounder study of the problem of knowledge. The older speculators had naively and dogmatically assumed the competence of the mind to reach truth; in denying the possibility of sure and universal knowledge, the Sophists forced philosophy to examine the thinking process itself and opened the way for a theory of knowledge. In employing all sorts of logical fallacies and sophisms, they made necessary a study of the correct laws of thought and hastened the birth of logic.
The same thing may be said of moral knowledge and practice. The appeal to the individual conscience was sound: from mere blind, unintelligent following of custom, morality was raised to the stage of reflective personal choice. When, however, the appeal became an appeal to mere subjective opinion and self-interest, it struck a false note. Independence of thought easily degenerates into intellectual and moral anarchy; individualism, into pure selfishness. Yet in this field, again, Sophistry rendered a service: radical criticism of the common notions of right and wrong and public and private justice, made necessary a profounder study of ethics and politics, — a study that was soon to bear wonderful fruit.
The great value of the entire Sophistic movement consisted in this: it awakened thought and challenged philosophy, religion, custom, morals, and the institutions based on them, to justify themselves to reason. In denying the possibility of knowledge, the Sophists made it necessary for knowledge to justify itself: they compelled philosophy to seek a criterion of knowledge. In attacking the traditional morality, they compelled morality to defend itself against skepticism and nihilism, and to find a rational principle of right and wrong. In attacking the traditional religious beliefs, they pressed upon thinkers the need of developing more consistent and purer conceptions of God. And in criticising the State and its laws, they made inevitable the development of a philosophic theory of the State. It became necessary to build upon more solid foundations, to go back to first principles. What is knowledge, what is truth? What is right, what is the good? What is the true conception of God? What is the meaning and purpose of the State and human institutions? And these problems, finally, forced the thinkers of Greece to reconsider, from new angles, the old question, which had been temporarily obscured, but which no people can long ignore: What is the world and man’s place in nature?
See also the Wikipedia article “Sophist“