Jonathan Sarna is the Joseph H. and Belle R. Braun Professor of American Jewish History at Brandeis University. His new book, "American Judaism," is out this month from Yale University Press.

The title of your book is "American Judaism," rather than "American Jews." Can you explain the difference?
There have been quite a few histories of American Jews-that is, the Jewish people in America. But strangely we have not had, in half a century, a serious work on American Judaism, the religion of American Jews. How has it developed? How has it changed? What is its relationship to American religion? How has it been influenced by American Protestantism? Where does it stand today?

People who study American religion really have very little sense of how Judaism fits in to that story. How Jews have been affected by the great turning points-the various awakenings, the Civil War, the women's movement, and so forth. American Judaism is distinctive. It's very different than Judaism is in Israel or Europe.

What are the major differences between Judaism in Europe and here?
The first thing is there's no chief rabbi in America. There was an experiment with one [in the 1840s], but it didn't last. The failure is more significant than the fact that they tried it.

Most chief rabbis are recognized, in some respect, by the government. That's true in England, in France, and certainly in Israel. There's an individual who represents the Jewish religion to the government, someone who stands opposite the cardinal or the archbishop. Indeed, what we have in Judaism here, as we also have in Christianity, is a kind of free market. There's no central authority that says you can only be Jewish this way and not another way.

The whole structure of American Judaism, with different movements or denominations and no central authority, suggests that American Judaism is influenced by Protestantism. Anybody is free, without seeking permission from any chief rabbi or any government office, to open up their own synagogue and to worship God as a Jew in the way that they think best. It is very much a reflection of church-state separation and the way religion developed in the wake of the American Revolution.

This free-market approach to Judaism has often run counter to the idea of Jewish unity, both now and in the past.
Yes, no question about it. The issues we think of as contemporary actually have very deep roots in the American Jewish experience. Some of them are problems that we have been grappling with, literally, for 350 years.

The question is: What holds everybody together? At a certain point in my research I realized that just as what holds Protestants together is basically the fact that they are not Catholic, what holds Jews together is basically the fact that they are not Christian. That's what unites Jews. But on many other issues, they are greatly divided.

But it seems like this idea of Jewish unity is much more important to Jews than the idea of Protestant unity is to Protestants.
I think that's right. Jews still do think of themselves as kind of one large family, and like any family, they are perturbed when unity is lacking. Religions that are ethnically based are much more concerned about unity, about sharing certain common memories and values and goals than religions that are not ethnically based.

Can you offer a few of the examples of the way Protestant movements have affected Judaism?
I think the notion that there are many paths to God and many ways of being a Protestant deeply affected Jews. The idea that any community will have people of varying churches is so basic to the way Americans think. [The Reform movement in Judaism] certainly referred to Protestant teachings to justify the reforms they sought to institute.

Judaism, like Protestantism, has also experienced eras of revival. Lots of people wrongly imagine that Jews came to this country Orthodox, that each generation is a little less religious, and that eventually they intermarry and march down the aisle of a church. That's not the Judaism that I found. Rather, periods of decline, periods of revival-much like we see in the history of American religion as a whole. Indeed, eras such as the second Great Awakening [from the 1790s to the 1840s] saw a great deal of new interest in Judaism, a back-to-the-synagogue movement-new excitement, new experimentation.

In our own day, just as American Protestants and Catholics have grappled first with the issue of women, and more recently with the issue of gays, so we find American Judaism grappling with these issues. The issues of immigration are the issues that all of our movements and faiths confronted. How do you Americanize? What do you retain? What do you lose? To what extent should we live in an enclave, to what extent should we reach out to those of other faiths? These are debates that go on throughout American religion.

Do you think that American Jews typically see themselves as part of this larger story?
No. I think American Jews really don't know much about their history at all and don't know too much about American religion. Until recently, American religion was a rather Christian subject, so Jews didn't study it. I think that American Jews have tended to understand themselves sociologically rather than historically. When issues come up, they commission a study or a poll, rather than saying, "Have we confronted this issue before? Is there something that we can learn from our past? Are there lessons from earlier Jews who confronted the same problem?"

In your book you write about several major challenges facing American Judaism in the future. Are there lessons we can learn from the past for any of those?
Yes...The question of contemporary culture, for one. This is probably the oldest tension in American Judaism. As soon as a minority faith decides it's not going to build a wall around itself, but is going to be part of a larger culture, it must decide how much to absorb from that larger culture, and what will define it as different. For example, even if contemporary culture says the day of rest is Sunday, Jews observe the day of rest on Saturday--that is going to be one of the distinctions between Judaism and the majority faith. That question is on an ongoing one. It long predates America actually.

In many respects, Judaism faces the Culture Wars that American society as a whole is going through. Gender equality, personal autonomy, gay and lesbian rights, and liberal American values--these pose new challenges to American Judaism. In many cases, although those are good American values, they're not really Jewish values. And the question is: Should some of those values be absorbed, or, in some cases, should those values be challenged? That's really the debate that is going on in the American Jewish community.

You need only read the Bible to see that the problem of Jewish unity was one that Moses confronted. The Book of Judges and the Book of Kings show that Jewish unity is probably the oldest problem in Jewish life. Nevertheless, I think the issues now are very serious ones, because there is no shared commitment to Jewish law in America.

Today's Jewish community doesn't even share a common Bible. Once upon a time, most Jews--Reform, Conservative, or Orthodox--used the one-volume edition of the Pentateuch, edited by Chief Rabbi Hertz in England. That was the standard commentary you found across the spectrum. Today we have an Orthodox Pentateuch, a Conservative Pentateuch, and a Reform Pentateuch. The text is the same, but the translations are different. Most importantly, the commentaries are very different, suggesting three entirely different approaches to the study of the Bible. In some ways, I think that is a very worrisome development.

Currently, there are both signs of danger and hopeful signs, both assimilation and revitalization. The message is that the future is really in the hands of the community. People shape American Judaism.

You write about a few issues that have fragmented Jewish movements, like the issue of women's ordination. Do you see the issue of gay rights as having a similar effect?
Yes, no question. In some ways it's more difficult because you're dealing there with a Biblical prohibition against homosexual relations. Some Jews believe the Bible governs sexual relations. Others believe that morality then and morality today are different, and that the underlying values of Judaism, values of caring for human beings and the like, mandate a change. Those two positions are very, very hard to reconcile, and my guess is that they won't be reconciled.

We will have movements that will embrace the gay lifestyle as simply an alternative mode of sexuality, and we will have movements that will insist that it is nothing less than sinful. There's really no possibility of a middle ground because it comes down to how you read the Bible and how much authority does it have. Does it have a veto? Or is it simply a historical record of the past?

So for some Jews, biblical text is the authority that is otherwise lacking in American Jews?
Yes, for those who accept it. I think for Orthodox Jews, Biblical authority and Jewish law, what is known as halakhah does in fact govern; it is the authority. If you want to know how to act, you act you ask what halakhah says. But it's only a small percentage of American Jews-less than 10 percent-who ask that question in their day-to-day lives.

When you talk about a divide into two groups of Jews, do you mean that 10 percent and everybody else?
It's hard to know how it would go, but I certainly think that it would be a traditional-liberal divide. People in the middle find themselves forced to choose which way they will go. The Conservative movement, which has historically been the middle in American Jewish religious life, is precisely that. Some if forced to choose will opt for tradition, and others if forced to choose would opt for change.

But I do not think that the future is pre-ordained here. Jews have come back from the brink many times. The split in Judaism, the idea that there would be two kinds of Jews, has been predicted many more times than it has come to pass. It's a self-negating prophecy. No sooner is the fear uttered than lots of people who believe that the unity of Jews is the greatest value of all, more important almost than any of the other issues, work to try to heal the breach and bring everybody closer to the center.