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De Officiis (On Duties or On Obligations) is a treatise by Marcus Tullius Cicero divided into three books, in which Cicero expounds his conception of the best way to live, behave, and observe moral obligations.
De Officiis was written in October–November 44 BC, in under four weeks. This was Cicero's last year alive, and he was 62 years of age. Cicero was at this time still active in politics, trying to stop revolutionary forces from taking control of the Roman Republic. Despite his efforts, the republican system failed to revive even upon the assassination of Caesar, and Cicero was himself assassinated shortly thereafter.
The essay was written in the form of a letter to his son with the same name, who studied philosophy in Athens. Judging from its form, it is nonetheless likely that Cicero wrote with a broader audience in mind. The essay was published posthumously.
De Officiis has been characterized as an attempt to define ideals of public behavior. It criticizes the recently overthrown dictator Julius Caesar in several places, and his dictatorship as a whole.
Although Cicero was influenced by the Academic, Peripatetic, and Stoic schools of Greek philosophy, this work shows the influence of the Stoic philosopher Panaetius. The essay discusses what is honorable (Book I), what is expedient or to one's advantage (Book II), and what to do when the honorable and expedient conflict (Book III). Cicero says they are the same and that they only appear to be in conflict. In Book III, Cicero expresses his own ideas. Michael Grant tells us that "Cicero himself seems to have regarded this treatise as his spiritual testament and masterpiece." 
Cicero claims that the absence of political rights corrupts moral virtues. Cicero also speaks of a natural law that is said to govern both humans  and gods alike.  Cicero urged his son Marcus to follow nature and wisdom, as well as politics, and warned against pleasure and indolence. Cicero's essay relies heavily on anecdotes, much more than his other works, and is written in a more leisurely and less formal style than his other writings, perhaps because he wrote it hastily. Like the satires of Juvenal, Cicero's De Officiis refers frequently to current events of his time.
The work's legacy is profound. Although not a Christian work, St. Ambrose in 390 declared it legitimate for the Church to use (along with everything else Cicero, and the equally popular Roman philosopher Seneca, had written). It became the moral authority during the Middle Ages. Of the Church Fathers, St. Augustine, St. Jerome and even more so St. Thomas Aquinas, are known to have been familiar with it. Illustrating its importance, some 700 handwritten copies remain extant in libraries around the world dating back to before the invention of the printing press. Only the Latin grammarian Priscian is better attested to with such handwritten copies, with some 900 remaining extant. Following the invention of the printing press, De Officiis was the third book to be printed—third only to the Gutenberg Bible and Donatus's "Ars Minor", which was the first printed book. 
Petrarch, the father of humanism and a leader in the revival of Classical learning, championed Cicero. Several of his works build upon the precepts of De officiis. The Catholic humanist, Erasmus, published his own edition in Paris in 1501. His enthusiasm for this moral treatise is expressed in many works. The German humanist, Philip Melanchthon established De officiis in Lutheran humanist schools.
T. W. Baldwin said that "in Shakespeare's day De Officiis was the pinnacle of moral philosophy". Sir Thomas Elyot, in his popular Governour (1531), lists three essential texts for bringing up young gentlemen: Plato's works, Aristotle's Ethics, and De Officiis.
In the 17th century it was a standard text at English schools (Westminster and Eton) and universities (Cambridge and Oxford). It was extensively discussed by Grotius and Pufendorf. Hugo Grotius drew heavily on De officiis in his major work, On the Law of War and Peace. It influenced Robert Sanderson and John Locke.
In the 18th century, Voltaire said of De Officiis "No one will ever write anything more wise". Frederick the Great thought so highly of the book that he asked the scholar Christian Garve to do a new translation of it, even though there had been already two German translations since 1756. Garve's project resulted in 880 additional pages of commentary.
In 1885, the city of Perugia was shaken by the theft of an illuminated manuscript of De Officiis from the city's Library Augusta. The chief librarian Adamo Rossi, a well-known scholar, was originally suspected but exonerated after a lengthy administrative and judicial investigation. The culprit in the theft was never found. Suspicion fell on a janitor who a few years later became well-to-do enough to build for himself a fine house. The former janitor's house was nicknamed "Villa Cicero" by residents of Perugia.
De Officiis continues to be one of the most popular of Cicero's works because of its style, and because of its depiction of Roman political life under the Republic.
PRINTING, an Art, as some say, first invented by Lawrence Coster of Haarlem in Holland, or as others say, by John Guttemburg in Germany, and brought into England by Caxton and Turner, who were sent by King Henry VI. to learn it: One of the first printed Books now extant is Tully's Offices, printed Anno 1465, and kept in the Bodleian Library at Oxford.
---An Universal Etymological English Dictionary. N. Bailey, 1724.
Chart showing the number of references in each month of the diary’s entries.