What exactly is race? In this book I borrow a clear definition given to me by Margot Minardi, a thoughtful and generous scholar who is studying the development of ideas about race in the 1700s. "Race" is a way of explaining human difference and organizing people into categories. It rests on four assumptions -- what I call "pillars":

1) Physical differences matter. The color of our skin, the curl of our hair, the size of our nose or lips -- these are important. How we look is not just a personal matter; it identifies us as part of a larger group.
2) These differences in our bodies cannot change. They are given to us at birth and remain fixed.
3) That is because they are inherited. Our personal features are actually the characteristics of our group, which are passed down from one generation to the next.
4) Each group has a distinct level of brain power and moral refinement, thus they are naturally and unchangeably ranked. Groups can be rated from more primitive to more advanced, more animal to more thoughtful, more savage to more civilized.

This whole book is devoted to tracing out how, in the Western world, these four ideas grew, developed, were linked together and came to be regarded as true. We have forgotten that we did not always have these beliefs, and that our ideas have changed over time. In fact, today "race" has become such a standard way of viewing people, we don't even have to think about it.
We "know" that people are the same, under the skin. Yet we "know" that the best athletes are black. We "know" that, in America, the real, deep, terrible racial division is between black and white. And yet Japanese Americans were put into internment camps during World War II for being neither black nor white. Jews were forced to remain in Europe, to be gassed and fed into ovens, because of their "race." Race is an uncomfortable reality, and yet the most brilliant scientists, doctors, and professors cannot agree on whether there are any races at all.
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I believe race is our modern way of handling emotions that go back to the very beginning of human evolution. That is one reason why race is so hard for us to deal with. In one way, race seems as current as science; in another it taps our oldest fears. ... There is no safe way to write about race.
I say "race," but I mean racism or racial prejudice. Even though the idea of race is a recent invention, fear and hatred of those who strike us as different is extremely ancient. That bears repetition: "Racial prejudice" and "hatred of difference" are not the same. For the great majority of human history we have taken slaves, slaughtered enemies, looked down on those who are different, without believing our victims were of different "races." Instead, we despised others as savages or barbarians; as weaklings or strangers; as pagans, Muslims, or Jews, Protestants or Catholics. I think that our deep feelings about race are the latest version of a mind-set that begins in infants and probably took shape at the very beginning of human evolution.

I have chosen not to frame this book as a study of how Jews became white, but as one that explores how Jews negotiated their place in a complex racial world where Jewishness, whiteness, and blackness have all made significant claims on them.