'On the Ends of Good and Evil' Summary

First and second books (Liber Primus and Liber Secundus) 

The first two books are a dialogue set at Cicero's country home in Cumae between himself and a young Epicurean named Lucias Torquatus, while another young Roman named Gaius 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.