Of his books, Thrasylus has given a regular catalog, in the same way that he has arranged the works of Plato, dividing them into four classes.
Now these are his ethical works: The Pythagoras; a treatise on the Disposition of the Wise Man; an essay on those in the Shades Below; the Tritogeneia (this is so called because from Minerva three things are derived which hold together all human affairs); a treatise on Manly Courage or Valor; the Horn of Amalthea; an essay on Cheerfulness; a volume of Ethical Commentaries. A treatise entitled For Cheerfulness, (εὐεστὼ) is not found.
These are his writings on natural philosophy: The Great World (which Theophrastus asserts to be the work of Leucippus); the Little World; the Cosmography; a treatise on the Planets; the first book on Nature; two books on the Nature of Man, or on Flesh; an essay on the Mind; one on the Senses (some people join these two together in one volume, which they entitle, On the Soul); a treatise on Juices; one on Colors; one on the Different Figures; one on the Changes of Figures; the Cratynteria (that is to say, an essay, approving of what has been said in preceding ones); a treatise on Phenomenon, or on Providence; three books on Pestilences, or Pestilential Evils; a book of Difficulties. These are his books on natural philosophy.
His miscellaneous works are these: Heavenly Causes; Aerial Causes; Causes Affecting Plane Surfaces; Causes Referring to Fire, and to What Is in Fire; Causes Affecting Voices; Causes Affecting Seeds, and Plants, and Fruits; three books of Causes Affecting Animals; Miscellaneous Causes; a treatise on the Magnet. These are his miscellaneous works.
His mathematical writings are the following: A treatise on the Difference of Opinion, or on the Contact of the Circle and the Sphere; one on Geometry; one on Numbers; one on Incommensurable Lines, and Solids, in two books; a volume called Explanations; the Great Year, or the Astronomical Calendar; a discussion on the Clepsydra; the Map of the Heavens; Geography; Polography; Actinography, or a discussion on Rays of Light. These are his mathematical works.
His works on music are the following: A treatise on Rhythm and Harmony; one on Poetry; one on the beauty of Epic Poems; one on Euphonious and Discordant Letters; one on Homer, or on Propriety of Diction and Dialects; one on Song, one on Words; the Onomasticon. These are his musical works.
The following are his works on art: Prognostics; a treatise on the Way of Living, called also Diaetetics, or the Opinions of a Physician; Causes relating to Unfavorable and Favorable Opportunities; a treatise on Agriculture, called also the Georgic; one on Painting; Tactics, and Fighting in Heavy Armour. These are his works on such subjects.
Some authors also give a list of some separate treatises which they collect from his Commentaries. A treatise on the Sacred Letters seen at Babylon; another on the Sacred Letters seen at Meroe; the Voyage Round the Ocean; a treatise on History; a Chaldaic Discourse; a Phrygian Discourse; a treatise on Fever; an essay on those who are attacked with Cough after illness; the Principles of Laws; Things Made by Hand, or Problems.
As to the other books which some writers ascribed to him, some are merely extracts from his other writings, and some are confessedly the work of others. And this is a sufficient account of his writings.
There were six people of the name of Democritus: The first was this man of whom we are speaking; the second was a musician of Chios, who lived about the same time; the third was a sculptor who is mentioned by Antigonus; the fourth is a man who wrote a treatise on the Temple at Ephesus, and on the city of Samothrace; the fifth was an epigrammatic poet, of great perspicuity and elegance; the sixth was a citizen of Pergamus, who wrote a treatise on Oratory.
Protagoras was the son of Artemon, or as Apollodorus says (which account is corroborated by Deinon, in his History of Persia) of Maeander. He was a native of Abdera, as Heraclides Ponticus tell us, in his treatise on Laws; and the same authority informs us that he made laws for the Thurians. But, according to the statement of Eupolis, in his Flatterers, he was a native of Teos; for he says:
Within you’ll find Protagoras, of Teos.
He, and Prodicus of Ceos, used to levy contributions for giving their lectures; and Plato, in his Protagoras, says that Prodicus had a very powerful voice.
Protagoras was a pupil of Democritus. And he was surnamed Wisdom, as Phavorinus informs us in his Universal History.
He was the first person who asserted that in every question there were two sides to the argument exactly opposite to one another. And he used to employ them in his arguments, being the first person who did so. But he began something in this manner: “Man is the measure of all things: of those things which exist as he is; and of those things which do not exist as he is not.” And he used to say that nothing else was soul except the senses, as Plato says, in the Theaetetus; and that everything was true. And another of his treatises he begins in this way: “Concerning the Gods, I am not able to know to a certainty whether they exist or whether they do not. For there are many things which prevent one from knowing, especially the obscurity of the subject, and the shortness of the life of man.” And on account of this beginning of his treatise, he was banished by the Athenians. And they burnt his books in the marketplace, calling them in by the public crier, and compelling all who possessed them to surrender them.
He was the first person who demanded payment of his pupils; fixing his charge at a hundred minae. He was also the first person who gave a precise definition of the parts of time; and who explained the value of opportunity, and who instituted contests of argument, and who armed the disputants with the weapon of sophism. He it was too who first left facts out of consideration, and fastened his arguments on words; and who was the parent of the present superficial and futile kinds of discussion. On which account Timon says of him:
Protagoras, that slippery arguer, In disputatious contests fully skilled.
He too it was who first invented that sort of argument which is called the Socratic, and who first employed the reasonings of Antisthenes, which attempt to establish the point that they cannot be contradicted; as Plato tells us in his Euthydemus. He was also the first person who practiced regular discussions on set subjects, as Artemidorus the dialectician, tells us in his treatise against Chrysippus. He was also the original inventor of the porter’s pad for men to carry their burdens on, as we are assured by Aristotle, in his book on Education; for he himself was a porter, as Epicurus says somewhere or other. And it was in this way that he became highly thought of by Democritus, who saw him as he was tying up some sticks.
He was also the first person who divided discourse into four parts: entreaty, interrogation, answer, and injunction; though some writers make the parts seven: narration, interrogation, answer, injunction, promise, entreaty, and invocation; and these he called the foundations of discourse; but Alcidamas says that there are four divisions of discourse: affirmation, denial, interrogation, and invocation.
The first of his works that he ever read in public was the treatise on the Gods, the beginning of which we have quoted above, and he read this at Athens in the house of Euripides, or as some say, in that of Megaclides; others say that he read it in the Lyceum; his pupil Archagoras, the son of Theodotus, giving him the aid of his voice. His accuser was Pythodorus, the son of Polyzelus, one of the four hundred; but Aristotle calls him Evathlus.
The writings of his which are still extant are these: a treatise on the Art of Contention; one on Wrestling; one on Mathematics; one on a Republic; one on Ambition; one on Virtues; one on the Original Condition of Man; one on those in the Shades Below; one on the Things which are not done properly by Men; one volume of Precepts; one essay entitled Justice in Pleading for Hire; two books of Contradictions.
These are his books.
Plato also addressed a dialogue to him.
Philochorus relates that as he was sailing to Sicily his ship was wrecked, and that this circumstance is alluded to by Euripides in his Ixion; and some say that he died on his journey, being about ninety years old. But Apollodorus states his age at seventy years, and says that he was a sophist forty years, and that he flourished about the eighty-fourth Olympiad. There is an epigram upon him written by myself, in the following terms:
I hear accounts of you, Protagoras, That, travelling far from Athens, on the road, You, an old man, and quite infirm, did die. For Cecrops’ city drove you forth to exile; But you, though ’scaping dread Minerva’s might, Could not escape the outspread arms of Pluto.