First and second books (Liber Primus and Liber Secundus) The first two books are a dialogue set at Cicero's home city of
Cumae between himself and
Lucius Manlius Torquatus, a young
Epicurean, while another young Roman,
Gaius Valerius Triarius, listens on. In the first book, the interlocutors present the Epicurean theory of
hedonism, which holds that pleasure in the form of
aponia (absence of pain) is regarded as the highest good. In the second book, Cicero criticizes this view, attacking the Epicurean definition of pleasure and arguing that it is inconsistent to hold pleasure as the absence of pain as the final good, since these are not one single good, but rather two distinct goods.
Third and fourth books (Liber Tertius and Liber Quartus) In the next two books,
Stoic ethics are discussed. In the third book, Cicero's interlocutor,
Marcus Porcius Cato, presents Stoic doctrine. Here, Cicero introduces the technical terms used by the Stoics into
Latin. The highest and only good of the Stoics is
virtue (moral good). In the fourth book, Cicero casts doubt on this
dogma, arguing a supposed natural state (the "cradle argument"), as well as issues regarding the exclusion of other goods entailed by Stoic doctrine.
Fifth book (Liber Quintus) In the last book, Cicero presents in the form of a dialogue between himself and several friends the theory of
eudaimonia taught by
Antiochus of Ascalon, which treats
Aristotelianism as a subgroup of
Platonism. This theory includes both virtue and external goods as the highest good. At the end of the book, Cicero criticized logical inconsistencies of this teaching, but more briefly and only addressing details, not broader principles. Cicero then declares that he follows this school of thought, albeit not without reservations, while respecting the valuable aspects of the teachings presented in the previous books. == Legacy ==