Pp. xi, 160 , Aldershot , Ashgate , 2007 , £50.00.

This book is essentially an account of why Plato, as an objectivist, should and did find relativism a real challenge. The account of relativism is attached to the work of Protagoras, as reflected above all in Plato's Protagoras and Theaetetus. Recent students of ancient philosophy have argued, pretty convincingly, that the historical philosopher Protagoras was not in any serious sense a relativist. Zilioli disagrees. His Protagoras emerges from the Platonic pages as a ‘robust’ relativist, committed to a far more wholehearted relativism than most scholars have tended to attribute to him. Zilioli also projects this robust relativism back on to the historical figure, which is a risky move, simply because he is basing himself almost entirely on the view of Protagoras's teaching constructed (or, perhaps, reconstructed) by Plato.

Leaving aside this historical issue, this is a really good book. It consists of a brief introduction, four substantial chapters, and a brief epilogue. Zilioli understands Protagoras's relativism as threefold: perceptual relativism is extended to ethical relativism and also to an epistemological relativism with ontological consequences, specifically that nothing exists except in relation to some person.

Chapter 1 teases out from the evidence of Theaetetus three core Protagorean beliefs: perceptual relativism, ontological indeterminacy, and perceptual privacy. At the same time, Zilioli argues (contrary to Burnyeat, and to my mind correctly) that this is as far down the line of what Plato claims are the consequences of perceptual relativism as we need to go: we do not also need to attribute Heraclitean flux to him. The most important points of this chapter are well stated; I disagree only with Zilioli's opinion that Sextus Empiricus is a witness to Protagoras's views independent of what Plato said in his dialogues.

In Chapter 2, Zilioli argues that Cratylus seems to conform the attribution of ontological indeterminacy to Protagoras, and hence ontological relativism, and does so without any mention of flux. (Again, though, Zilioli should have taken into account that Plato wrote both Theaetetus and Cratylus, so that it is hard to take this is external evidence for Protagoras's views.) Plato's defence of Protagoras (Theaetetus 166a–168c) is then analysed in a way that fits with his relativism and makes reasonable sense. Zilioli rightly stresses that by ‘perception’ Protagoras means to include all cognitive activities, and he argues that the defence is essentially the kind of thing Protagoras might have said, by comparing two fragments (DK 6a and 6b). Here, I think, Zilioli is stretching a point: the two fragments are so slight as to offer little real help. He also argues (with the help of Kuhn and Feyerabend) that Protagoras's position is philosophically coherent and interesting. The incommensurability that critics find damning for relativism is mitigated by the fact that a relativist can give real meaning to terms over time by seeing how others react to the same situations to which he is reacting himself. Protagoras resembles an empiricist.

For Chapter 3, passages not just of Theaetetus but also Protagoras become relevant, as Zilioli explores Protagoras's extension of cognitive relativism into ethical relativism: that societies can and do decide their own moral norms. Zilioli has to argue for his ‘integrated reading’ (93) of the relevant passages, because according to Protagoras, each and every society depends for its existence on justice and respect, which appear to be objective standards. But Zilioli argues that different societies understand ‘justice and respect’ differently.

From time to time in the first three chapters, Zilioli has taken Plato to task for underestimating Protagoras's position. The final chapter then argues that Plato's own responses to Protagoras are not as strong as they are usually taken to be. Zilioli argues well that Plato's objections – first, that Protagoras must recognize at least some objective standards, such as health and expediency, and second, that relativism is self-refuting – are scarcely decisive, and are flawed in themselves. But this chapter contains by far the weakest argument of the book, which Zilioli would have done well to have omitted (I don't think it adds substantially to his case). He argues (116–18) that Protagoras cannot be charged with inconsistency since he ‘shows’ his relativism rather than ‘saying’ it. But of course we are concerned, as Zilioli himself has been, with Protagoras's theories as spelled out, so Zilioli needs a far stronger reason for acquitting Protagorean relativism of the usual charge of inconsistency.

In this review I have focused on the book as a work of ancient philosophical exegesis, but Zilioli is also concerned to defend relativism as a philosophical position, and he introduces modern philosophical debates to deepen our understanding of Protagoras, and to assess the strengths and weaknesses of his views. As I have already implied, I believe that the book is better as an exegesis of Plato than as an attempt to uncover the views of the historical Protagoras. Finally, I should say that Zilioli, from the University of Parma, seems to have written the book in English himself; occasionally, it shows.