In those turbulent days when Caesar crossed the Rubicon, conquered Pompey, and made himself dictator, Cicero retired for a moment from political life and sought solace in reading and writing philosophy. “Remember,” he begged Atticus, “not to give up your books to anybody, but to keep them, as you promised, for me. I entertain the strongest affection for them, as I now feel disgust for everything else.” In his youth, defending the poet Archias in the most modest and amiable of his speeches, he had praised the study of literature as “nourishing our adolescence, adorning our prosperity, and delighting our old age.” Now he took his own counsel, and in little more than two years wrote almost a library of philosophy. The dissolution of religious belief in the higher classes had left a moral vacuum, by which Rome seemed to be drawn into a disintegration of character and society. Cicero dreamed that philosophy might serve as a substitute for theology in providing for these classes a guide and stimulus to right living. He resolved not to construct one more system, but to summarize the teachings of the Greek sages and offer them as his last gift to his people. He was honest enough to confess that he was for the most part adapting, sometimes translating, the treatises of Panaetius, Poseidonius, and other recent Greeks. But he transformed the dull prose of his models into limpid and graceful Latin, enlivened his discourse with dialogue, and passed quickly over the deserts of logic and metaphysics to the living problems of conduct and statesmanship. Like Lucretius he had to invent a philosophical terminology; he succeeded, and put both language and philosophy heavily in his debt. Not since Plato had wisdom worn such prose.

It was from Plato above all that his ideas stemmed. He did not relish the dogmatism of the Epicureans, who “talk of divine things with such assurance that you would imagine they had come directly from an assemblage of the gods”; nor yet that of the Stoics, who so labor the argument from design that “you would suppose even the gods had been made for human use”- a theory that Cicero himself, in other moods, would not find incredible. His starting point is that of the New Academy- a lenient skepticism which denied all certainties and found probability sufficient for human life. “In most things,” he writes, “my philosophy is that of doubt…. May I have your leave not to know what I do not know?” “Those who seek to learn my personal opinion,” he says, “show an unreasonable degree of curiosity”; but his coyness soon yields to his talent for expression. He scorns sacrifices, oracles, and auguries, and devotes an entire treatise to disproving divination. Against the widespread cult of astrology he asks if all the men slain at Cannae had been born under the same star. He even doubts that a knowledge of the future would be a boon; the future may be as unpleasant as much else of the truth that we so recklessly chase. He vainly thinks to make short work of old beliefs by laughing them out of court: “When we call corn Ceres and wine Bacchus we use a common figure of speech; but do you imagine that anybody is so insane as to believe that the thing he feeds upon is a god?” Nevertheless, he is as skeptical of atheism as of any other dogma. He rejects the atomism of Democritus and Lucretius; it is as unlikely that unguided atoms- even in infinite time- could fall into the order of the existing world as that the letters of the alphabet should spontaneously form the Annales of Ennius. Our ignorance of the gods is no guarantee of their nonexistence; and indeed, Cicero argues, the general agreement of mankind establishes a balance of probability in favor of Providence. He concludes that religion is indispensable to private morals and public order and that no man of sense will attack it. Hence, while writing against divination, he continued to fulfill the functions of official augur. It was not quite hypocrisy; he would have called it statesmanship. Roman morals, society, and government were bound up with the old religion and could not safely let it die. (The emperors would reason so in persecuting Christianity.) When his beloved Tullia died, Cicero inclined more strongly than ever to the hope of personal immortality. Many years before, in the “Dream of Scipio” with which he ended his Republic, he had borrowed from Pythagoras, Plato, and Eudoxus a complex and eloquent myth of a life beyond the grave, in which the good great dead enjoyed eternal bliss. But in his private correspondence- even in the letters that condoled with bereaved friends- there is no mention of an afterlife.