In this medium-length but magisterial treatment, Cohen seeks the causes of convivencia and the relatively happier lot of Jews under the domination of Islam contrasted with under Christianity during the Middle Ages. His findings are nuanced, equivocal and satisfyingly multi-factored. What he does is to look into causes. What he does not do is try to measure the relative tolerance of the two religious hegemons or ask whether one was more tolerant - he takes this almost as given and seeks to explain it. I regard this as a perfectly legitimate exercise and a perfectly sound starting point, but some reviewers have made it a criticism. If one were trying to rank the two hegemons this criticism would, of course, be perfectly fair, but Gay is not seeking to do this. He is starting from the observation of greater tolerance and looking for reasons.
Of course, "tolerance" is an equivocal term, and the difference is not as clear-cut as some would have one believe. The traditional "lachrymose" (tearful) model of Jewish life under Christianity is not the whole story, nor is that of the Golden Age of Samuel ibn Nagrela in Ha Sefarad. Jews living under Christianity in Southern Europe suffered far less persecution than those in the North; Jews living under the Almohads in North Africa were forced to convert to Islam. And then there is Granada and the fate of the Bani Quryaza. Tellingly, though, these last two are generally the only major pogroms that critics of Islam can name, whereas in Europe they were at times systematic and at others an endemic and recurring hazard. The Jews of North Africa, interestingly, appear to have remained crypto-Jews and to have returned to their religion when Almohad fanaticism subsided, whereas Christian-Muslim converts remained Muslim. Quite why this was the case is not explained to my satisfaction.
So how does Cohen explain tolerance? Well, as I stated his conclusions are satisfyingly multidimensional. There are circumstantial factors. For instance, Jews were only one of many groups of Dhimmi under Islam, but were the only divergent religious group permitted to survive at all under Christianity with the Augustinian doctrine of "witness" and immiseration, thus receiving the full attention of its spasms of intolerance. There are cultural and economic factors predating the respective religious hegemonies - for instance, that the Arabs were already a mercantile culture prior to Islam and had no strong prejudice against the foreign merchant. There were similar factors post-dating the hegemonies, such as that Jews were restricted by a variety of ordnances and commands to roles like that of moneylender under Christianity, whereas under Islam they were fully integrated into the trades at all levels and in all spheres. Also, Muslim and Dhimmi could intermarry and the spouse legally retain her religion - at least at most times. While a Dhimmi could not be the equal of a Muslim as a consequence of Islam's Establishment, much as a minority can never be truly equal today in a state with an Established church - and I speak as a humanist from a country with a Church of England and seats in government for bishops - he could be the business partner or customer, friend or spouse, and often was. Making money together is a strong antidote to bigotry.
Then, there are religious and foundational factors, and here Cohen offers an interesting interpretation of the butchery of Bani Qurayza. Yes, Islam began with confrontations with Jews at its inception. Yes, they are identified as an enemy. However, they are a defeated enemy. The Prophet of Islam killed the Jews; the Jews killed the Prophet of Christianity. (Sorry to put this as if the old libel were legitimate, but this is the differing thinking of the hegemons in a nutshell.) Christians have tended to go through phases of wanting revenge. Muslims have never felt the need.
Cohen's work is serious in its intent and wide in its scope. It does, however, by its very nature in studying the Middle Ages leave some important questions open. Some of them are urgent. Why have Jews largely been integrated since the Englightenment? Why was that integration suddenly shattered in the Shoah by a political movement that did not make an especially religious issue of murdering Jews? (In fact, a purely racial one.) Why has anti-Semitism started to burgeon in the Muslim world since the 19th Century? Cohen hints at some resolutions such as the changing nationalist model of the Muslim world. Pan-Arabism and straightforward nationalism are alien to Islam, with its model of the global Ummah and its exemptions and protections for Dhimmi. Now that Western-style, secular nation nation states have arisen, starting in the 19th Century, it is possible to see Dhimmi as a fifth column.
Moreover, there is an apparently intractable conflict in the Levant. Perhaps if we understand convivencia we can understand how the conflict can be resolved to the satisfaction of all parties? Well, maybe. Islam sees itself as the legitimate hegemon. It has lived in tolerance with other monotheisms, but on the understanding that they did not get above themselves. Even in the secular West a subordinate status raises recurrent tensions among more radical Muslims. Persuading them to accept a monotheistic hegemony not of their making on the site of the Rock itself may be a long haul. At any rate, Cohen's thorough and weighty contribution to understanding historic tolerance is an admirable contribution to the discussion.