In Book 1 of On divination, Cicero’s brother Quintus, who is not a Stoic, presents the Stoic case that all the many forms of divination at Rome are channels of divine communication. He does so explicitly in response to the arguments of On the nature of the gods, to strengthen the case that the gods care for us. I argue that his speech, which scholars have often called confused, can be better understood once we see it as a continuation of On the nature of the gods. For he speaks about not the, or even one, Stoic defence of divination, but rather two different Stoic views. The first is the view of Chrysippus, according to which divination was an art of interpreting messages from the gods. This view was challenged by the skeptic Carneades, and Cotta reissued some of this challenge in On the nature of the gods. Quintus recruits a new view in answer to this challenge, according to which some divination (e.g. augury, haruspicy, astrology) is artificial in that its divination meaning is first discovered by an art, but some is natural, in that some dreams and oracles have divinatory meaning without the use of an art.

Cicero says that almost no philosophers held atheism or agnosticism. For him the Central Question of philosophy of religion is not the existence of the gods, but whether the gods care for us by providence. He says we must answer this question to moderate religion. I argue that although traditional Roman pagan religion required orthopraxy, and not orthodoxy, Cicero thinks that the actions of a pagan practitioner could be "moderated" by what she believed about her religious behavior: if she believes that the gods care for us more than they do, that is superstition, but if she believes that they care for us less than they do, that is impiety. Yet Romans, Cicero says, were bewildered by their ancestral religion. He offers Hellenistic philosophy as a new route to responsible beliefs about it. Philosophy might help a Roman form true beliefs on the Central Question, or (like Cicero) to refrain from risky beliefs either way. On the nature of the gods and On divination are carefully designed to present this debate, among Stoics, with rich theories that the gods care and give us divinatory information, Epicureans, with rich theories to the contrary, and Academics, who withhold judgment.

Nineteenth and early twentieth century scholars thought Cicero a bad source for Hellenistic philosophy. They thought that the speeches in his dialogues were translated, often badly, from single sources. Thus they read him only to reconstruct his sources by Quellenforschung. I first give a sympathetic account of these scholars’ projects, which is often dismissed too easily today. Second, I give a complete argument that these scholars were wrong, and that today’s more positive, but often incompletely defended, view of Cicero is correct. Third, I argue that Cicero wrote dialogues not only to introduce Hellenistic philosophy to a Latin audience, but also as literary unities to impress a learned Roman audience who already knew philosophy in Greek. His models for the dialogue form were Plato, Aristotle, and Heraclides of Pontus, but he adapted it to to serve his radical Academic skepticism, in which he followed Carneades and Clitomachus. He hoped to be the model for a Latin tradition of good writing about philosophy, that would "illuminate" both philosophy and Latin. Cicero’s creativity as a philosophical author shows why Quellenforschung failed, and that he is a good source for Hellenistic thought.

Being a radical Academic skeptic, Cicero as author does not endorse an answer to the questions of On the nature of the gods and On divination. But when he portrays himself as a character in the dialogues, he portrays himself as finding plausible on those occasions a consistent philosophicaltheology and view of religion. I suggest that this is meant to model the free reaction of a skeptical mind to debates on questions where the skeptic forms no beliefs. The view that Cicero portrays as plausible to "himself" is the Stoic theology that the natural world is divine and benevolent, except that he finds implausible the Stoic view that divination delivers information from the gods (although he says that divinatory practices at Rome should continue for other reasons). Taking this attitude would be one way to "moderate" Roman religion, that is, to avoid impiety and superstition in practising it, but the reader is left free to make up his or her own mind.

In Book 1 of Cicero’s On the nature of the gods, Velleius argues for an Epicurean theology and view of religion. Cotta, an Academic skeptic, argues against him. I argue that when we see Cicero’s creative hand adapting Epicurean texts like the On Piety found at Herculaneum and attributed to Philodemus, we find that Velleius’ speech may be understood as proceeding from our allegedly natural concept that the gods are eternal and happy. Velleius’ seemingly intemperate criticism of his opponents, that they are crazy, follows from his position that they have somehow gone against this natural concept. His positive view, which proceeds from the happiness or blessedness (beatitudo, beatitas, eudaimonia) of the gods, is that Roman religion may be reinterpreted as worship of gods who do not care about us at all, and thus are ideals for us of the hedonist life free from pain. Despite Cicero’s habitual contempt for Epicureanism, he paints an attractive picture of Velleius’ spirituality. But Cotta argues that by making the gods not care for us, Epicurus has torn out the heart from religion, since he has made gods who are (so Cotta argues) selfish and not worthy of worship or imitation.

In Book 2 of On divination, Cicero’s own character attacks Quintus’ speech from Book 1, which argued that the gods give us information through our divinatory practices. Cicero, as a skeptic, aims to frustrate rash assent to Quintus’ view. He is an augur, a Roman state diviner. In the speech, he says that an augur may give the arguments he does, because augury, though often misunderstood, is not supposed to be a divinatory practice. The speech is in two parts. In the first, Cicero attacks Quintus’ argument that divination is a way to foretell chance events, on the grounds that Quintus speech is also founded on Stoic determinism. I argue that Cicero’s speech is unfair in its treatment of Quintus’ understanding of chance. In the second part, often using statistical and rhetorical arguments, Cicero concedes that Quintus’ stories of true divinatory predictions are accurate, but argues that this data cannot prove that divinatory practices reliably yield information from the gods. Scholars have often accused Cicero of arguing against straw men in this speech. I concede that this is sometimes so, but argue that this fact does not refute my overall case that On divination is a creative unity.