Themistius (Greek: , Themistios; 317, Paphlagonia - c. 390 AD, Constantinople), named (eloquent), was a statesman, rhetorician, and philosopher. He flourished in the reigns of Constantius II, Julian, Jovian, Valens, Gratian, and Theodosius I; and he enjoyed the favour of all those emperors, notwithstanding their many differences, and the fact that he himself was not a Christian. He was admitted to the senate by Constantius in 355, and he was prefect of Constantinople in 384 on the nomination of Theodosius. Of his many works, thirty-three orations of his have come down to us, as well as various commentaries and epitomes of the works of Aristotle.
He was born in Paphlagonia and taught at Phasis. Apart from a short sojourn in Rome, he resided in Constantinople during the rest of his life. He was the son of Eugenius, who was also a distinguished philosopher, and who is more than once mentioned in the orations of Themistius. Themistius was instructed by his father in philosophy, and devoted himself chiefly to Aristotle, though he also studied Pythagoreanism and Platonism. While still a youth he wrote commentaries on Aristotle, which were made public without his consent, and obtained for him a high reputation. He passed his youth in Asia Minor and Syria. He first met with Constantius II when the emperor visited Ancyra in Galatia in the eleventh year of his reign, 347, on which occasion Themistius delivered the first of his extant orations, Peri Philanthropias. It was not long after that he moved to Constantinople, where he taught philosophy for twenty years. In 355 he was made a senator; and the letter is still extant, in which Constantius recommends him to the senate, and speaks in the highest terms both of Themistius himself and of his father. We also possess the oration of thanks which Themistius addressed to the senate of Constantinople early in 356, in reply to the emperor's letter. In 357 he recited in the senate of Constantinople two orations in honour of Constantius, which were intended to have been delivered before the emperor himself, who was then at Rome. As a reward, Constantius conferred upon him the honour of a bronze statue; and, in 361, he was appointed to the praetorian rank by a decree still extant. In 358-359, Themistius may have served as proconsul of Constantinople in 358; he was the last to hold that office, before the position was elevated to the status of urban prefect.
Constantius died in 361; but Themistius, as a philosopher and non-Christian, naturally retained the favour of Julian, who spoke of him as the worthy senator of the whole world, and as the first philosopher of his age. The Suda states that Julian made Themistius prefect of Constantinople; but this is disproved by the speech delivered by Themistius, when he was really appointed to that office under Theodosius. Shortly before the death of Julian in 363, Themistius delivered an oration in honour of him, which is no longer extant, but which is referred to at some length by Libanius, in a letter to Themistius. In 364 he went, as one of the deputies from the senate, to meet Jovian at Dadastana, on the border of Galatia and Bithynia, and to confer the consulate upon him; and on this occasion he delivered an oration, which he afterwards repeated at Constantinople, in which he claims full liberty of conscience to practice any religion. In the same year he delivered an oration at Constantinople, in honour of the accession of Valentinian I and Valens, in the presence of the latter. His next oration is addressed to Valens, congratulating him on his victory over Procopius in June 366, and interceding for some of the rebels; it was delivered in 367. In the next year he accompanied Valens to the Danube in the second campaign of the Gothic war, and delivered before the emperor, at Marcianopolis, a congratulatory oration upon his Quinquennalia, 368. His next orations are to the young Valentinian II upon his consulship, 369, and to the senate of Constantinople, in the presence of Valens, in honour of the peace granted to the Goths, 370. On March 28, 373, he addressed to Valens, who was then in Syria, a congratulatory address upon the emperor's entrance on the tenth year of his reign. It was also while Valens was in Syria, that Themistius addressed to him an oration by which he persuaded him to cease from his persecution of the Catholic party. In addition to these orations, which prove that the orator was in high favour with the emperor, we have the testimony of Themistius himself to his influence with Valens.
In 377 we find him at Rome, where he appears to have gone on an embassy to Gratian, to whom he there delivered his oration entitled Erotikos. On the association of Theodosius I in the empire by Gratian, at Sirmium, in 379, Themistius delivered an elegant oration, congratulating the new emperor on his elevation. Of his remaining orations some are public and some private; but few of them demand special notice as connected with the events of his life. In 384, (about the first of September), he was made prefect of Constantinople, an office which had been offered to him, but declined, several times before. He only held the prefecture a few months, as we learn from an oration delivered after he had laid down the office, in which he mentions, as he had done even six years earlier, and more than once in the interval, his old age and ill-health. From the thirty-fourth oration we also learn that he had previously held the offices of princeps senatus and praefectus annonae, besides his embassy to Rome; in another oration he mentions ten embassies on which he had been sent before his prefecture; and in another, composed probably about 387, he says that he has been engaged for nearly forty years in public business and in embassies. So great was the confidence placed in him by Theodosius, that, though Themistius was not a Christian, the emperor, when departing for the West to oppose Magnus Maximus, entrusted his son Arcadius to the tutorship of the philosopher, 387-388. Nothing is known about Themistius after this time; and he may have died around 390. Besides the emperors, he numbered among his friends the chief orators and philosophers of the age, Christian and non-Christian. Not only Libanius, but Gregory of Nazianzus also was his friend and correspondent, and the latter, in an epistle still extant, calls him the "king of arguments."
The orations of Themistius, extant in the time of Photius (9th century), were thirty-six in number. Of these, thirty-three have come down to us in Greek. Two of them, however, (Orations 23 and 33, and perhaps Oration 28) are not fully preserved, and one (Oration 25) is a brief statement, not a full oration. Modern editions of the Orations have thirty-four pieces, because a Latin address to Valens has been included as Oration 12. It is now believed though that this Latin address is a 16th-century creation. The final oration (Oration 34) was discovered as recently as 1816 by Angelo Mai in the Ambrosian Library at Milan. There are, in addition, a few other fragments which may come from lost Orations, as well as an additional work which survives in Syriac and another preserved in Arabic.
The philosophical works of Themistius must have been very voluminous; for Photius tells us that he wrote commentaries on all the books of Aristotle, besides useful abstracts of the Posterior Analytics, the books On the Soul, and the Physics, and that there were works of his on Plato; "and, in a word, he is a lover and eager student of philosophy." The Suda mentions his epitome of the Physics of Aristotle, in eight books; of the Prior Analytics, in two books; of the Posterior Analytics, in two books; of the treatise On the Soul, in seven books; and of the Categories in one book.
The epitomes which survive are:
In addition to these works, two surviving anonymous paraphrases were mistakenly attributed to him in the Byzantine era, and are now assigned to a Pseudo-Themistius:
His paraphrases of Aristotle's Posterior Analytics, Physics and On the Soul are valuable; but the orations in which he panegyrizes successive emperors, comparing them to Plato's true philosopher, and even to the idea itself, are intended to flatter. Boëthius describes him as, disertissimus (or diligentissimus) scriptor ac lucidus, et omnia ad facilitatem intelligentiae revocans.
In philosophy Themistius was an eclectic. He held that Plato and Aristotle were in substantial agreement, that God has made men free to adopt the mode of worship they prefer, and that Christianity and Hellenism were merely two forms of the one universal religion.