I am also working on a book project as part of my British Academy Fellowship.
The purpose of my monograph is twofold: first, it reconstructs a sophistic debate about the value of justice that occurred in the second half of the 5th Century BCE and, second, it argues that this debate exerted a significant influence on Plato’s philosophy in the following century, especially as developed in his Republic. A more detailed chapter-by-chapter outline is appended below, but briefly: the first part of the book (Chapters One, Two, and Three) argues that in the 5th Century there was a highly sophisticated debate about justice and the extent to which it contributed to the individual’s prospering [εὐδαιμονία]. This debate took off when one group of sophists applied a new secular and naturalistic worldview to conventional ideas about morality and concluded that absent the gods who were traditionally thought to punish bad behavior, it was often more profitable for the individual to practice injustice than be scrupulously just. Another group of sophists responded to this first group by offering highly innovative arguments to defend the traditional idea that virtue is profitable without appealing to the interventionist gods. By discussing both groups of thinkers in turn, I show that there was a genuine philosophical debate about the value of justice in the 5th Century. The second part of the book (Chapters Four, Five, and Six) argues that Plato was both influenced by this debate and actively contributed to it in his Republic. Chapters Four and Five make the case for thinking that the central argument of the dialogue, including the famous division of goods, should be understood as Plato’s attempt to demonstrate the value of justice and settle the earlier debate once and for all. Chapter Six draws on the findings of the first part of the book to highlight two particular arguments made by Socrates that were influenced by the moral philosophy of the sophists in an especially direct way.
A more detailed chapter-by-chapter breakdown can be found here. Those interested in reading draft chapters of the chapters can email me from the contact page.
Here is a link to one of the manuscripts I have been looking at for the book!