All the letters of Greek and Roman origin which have come down to us seem to be doubtful, except those of Plato and Isocrates, until the days of Cicero. Under his genius the mind of the Roman nation took a sudden spring, and the polite literature of the world was embellished by epistolary composition. As the rules and illustrations of poetic writing were borrowed by Aristotle from the example of Homer, so the practice and authority of Cicero appear to have furnished precepts best entitled to determine the character and merits of the epistolary style. He esteemed it as a species of composition enjoying the privilege of great ease and familiarity, as well in its diction as in its treatment of its subject, and also in its employment of the weapons of wit and humor. The general style most suitable to its spirit and character he considered to be that most in use in the ordinary and daily intercourse of society. He admired a simple and playful use of language, and he affected, as he asserts, a common and almost plebeian manner of writing, using words of every-day stamp in his correspondence. In his view of letter writing, its style and manner ought to vary with the complexion of its subject matter, and be subjected to no abstract system of rules. Ho propounds three principal kinds of epistles: first, that which merely conveys interesting intelligence, being, as he says, the very object for which the thing itself came into existence; second, the jocose letter; third, the serious and solemn letter. And it was besides the opinion of the great orator--an opinion sanctioned and ratified by all honorable persons then and in our own day--that there is something sacred in the contents of a letter which gives it the strongest claims to be withheld from third persons. 'For who,' he exclaims, in his second Philippic, 'who that is at all influenced by good habits and feelings, has ever allowed himself to resent an affront or injury by exposing to others any letters received from the offending persons during their intercourse of friendship?' 'What else,' he eloquently exclaims, 'would be the tendency of such conduct but to rob the very life of life of its social charms! How many pleasantries find their way into letters, as amusing to the correspondents as they are insipid to others; and how many subjects of serious interest, which are entirely unfit to be brought before the public!'