His treatise _De Divinatione_ is conveyed in a discussion between his brother Quintus and himself, in two books. In the former, Quintus, after dividing Divination into the heads of natural and artificial, argues with the Stoics for its sacred nature, from the evidence of facts, the agreement of all nations, and the existence of divine intelligences. In the latter, Cicero questions its authority, with Carneades, from the uncertain nature of its rules, the absurdity and uselessness of the art, and the possibility of accounting from natural causes for the phenomena on which it was founded. This is a curious work, from the numerous cases adduced from the histories of Greece and Rome to illustrate the subject in dispute. His treatise _De Fato_ is quite a fragment; it purports to be the substance of a dissertation in which he explained to Hirtius (soon after Consul) the sentiments of Chrysippus, Diodorus, Epicurus, Carneades, and others, upon that abstruse subject. It is supposed to have consisted at least of two books, of which we have but the proem of the first, and a small portion of the second. In his beautiful compositions, _De Senectute_ and _De Amicitia_, Cato the censor and Laelius are respectively introduced, delivering their sentiments on those subjects. The conclusion of the former, in which Cato discourses on the immortality of the soul, has been always celebrated; and the opening of the latter, in which Fannius and Scaevola come to console Laelius on the death of Scipio, is as exquisite an instance of delicacy and taste in composition as can be found in his works. In the latter he has borrowed largely from the eighth and ninth books of Aristotle's _Ethics_. His treatise _De Officiis_ was finished about the time he wrote his second Philippic, a circumstance which illustrates the great versatility of his mental powers. Of a work so extensively celebrated, it is enough to have mentioned the name. Here he lays aside the less authoritative form of dialogue, and, with the dignity of the Roman Consul, unfolds, in his own person, the principles of morals, according to the views of the older schools, particularly of the Stoics. It is written in three books, with great perspicuity and elegance of style; the first book treats of the _honestum_, or _virtue_, the second of the _utile_, or _expedience_, and the third adjusts the claims of the two, when they happen to interfere with each other. His _Paradoxa Stoicorum_ might have been more suitably, perhaps, included in his rhetorical works, being six short declamations in support of the positions of Zeno; in which that philosopher's subtleties are adapted to the comprehension of the vulgar, and the events of the times. The second, fourth, and sixth, are respectively directed against Antony, Clodius, and Crassus. They seem to have suffered from time.[224] The sixth is the most eloquent, but the argument of the third is strikingly maintained.