What's the difference between a tailor and a doctor? A generation.

You get the joke, with its implications for neatly summarizing the immigrant experience, but the choice of a tailor to represent the past is one of the things that makes this a particularly Jewish joke. The preponderance of Jews in the international shmata business (the rag trade) is no coincidence, and is due to a strange combination of forces: biblical injunctions, anti-Semitic acts and bad luck.

Throughout Jewish history, most Jewish communities had at least one tailor, and often disproportionately more, relative to the size of the population. Apart from the practical necessity of having an expert in the creation and repair of clothing, it was also necessary for the observance of mitzvot (commandments) such as sha'atnez, the mysterious biblical injunction against wearing fabrics that combine wool and linen.

Economic factors often led to the large numbers of Jews in garment-related fields. The role of Jews in the money-lending trade of medieval Christian societies and their involvement in the trade of second-hand goods required some knowledge of tailoring. It was vital to keep pawned or old clothes meant for resale in good repair.

Also, the dictates of authorities, like the medieval church, enforced the wearing of distinctive garments by Jews, such as the pointed hat known in Western Europe as the Judenhut or the full-length black cape in Spain. The communities that lived under Islamic rule were restricted to the wearing of black clothing, as in North Africa, almost up to the 20th century.

But there was something else that kept Jews in the shmata business over the centuries: bad luck. Think Anatevka in "Fiddler on the Roof," and you'll remember that even Tevye had a tailor in the family (the ne'er-do-well Motel Kamzoil, whose wedding to Tzeitel ended in a pogrom and an encore). The plethora of tailors was also reflected in popular culture, as in the popular expression amkho sher un ayren ('the simple people of the scissors and ironing board'), which became in Yiddish literature a way of describing the Jews in the shtetl.

The phenomenon is also illustrated in a tale from the fabled town of clever idiots, Chelm. The cobbler of Chelm learned that his wife was unfaithful. He catches her with her lover and kills them both. The rabbinic court of Chelm decides to impose the death penalty. Joseph, the town dissenter, argues: "But he's our only cobbler. If we hang him, who will fix our shoes?" The head rabbi thinks. "I have a solution. True, we have only one cobbler, but we have two tailors. We'll hang one of them instead!"

Eventually, Jews went from selling old clothes to becoming retailers, manufacturers and wholesalers, and ultimately key figures in the modern clothing industry throughout Europe and America. By 1970 things had changed and Jews no longer held sway in the clothing industry. Like most successful immigrant stories (and jokes), many of the tailors took on white-collar jobs. And yet, the jokes remain, remnants (as it were) of bygone days, when the premise of jokes, such as this one, might have reflected a kernel of reality:

A newly opened shopping center had three tailors, all with shops next to each other. In another coincidence, all three tailors were named Jacob Silverstein. The first tailor put up a sign over his shop that proclaimed: "Jacob Silverstein — High Class Tailor."

Not to be outdone, the second tailor put up a sign saying: "Silverstein — Best Tailor Around."

The third tailor's sign was smaller but said: "Silverstein's Tailors — Main Entrance."