Until the eighteenth century, there was basically only one kind of Judaism, that which is now called Orthodox. It meant living by the religion’s 613 laws, and doing so suffused Jews’ lives with their faith. Then, starting with the thinker Baruch Spinoza (1632-77) and moving briskly during the Haskala, or “enlightenment,” from the late eighteenth century, Jews developed a wide variety of alternate interpretations of their religion, most of which diminished the role of faith in their lives and led to a concomitant reduction in Jewish affiliation.
These alternatives and other developments, in particular the Holocaust, caused the ranks of the Orthodox to be reduced to a small minority. Their percentage of the total world Jewish population reached a nadir in the post-World War II era, when it declined to about 5%.
The subsequent 60 years, however, witnessed a resurgence of the Orthodox element. This was, again, due to many factors, especially a tendency among the non-Orthodox to marry non-Jews and have fewer children. Recent figures on America published by the National Jewish Population Survey also point in this direction. The Orthodox proportion of American synagogue members, for example, went from 11% in 1971 to 16% in 1990 to 21% in 2000-01. (In absolute numbers, it bears noting, the American Jewish population went steadily down during these decades.)
Should this trend continue, it is conceivable that the ratio will return to roughly where it was two centuries ago, with the Orthodox again constituting the great majority of Jews. Were that to happen, the non-Orthodox phenomenon could seem in retrospect merely an episode, an interesting, eventful, consequential, and yet doomed search for alternatives, suggesting that living by the law may be essential for maintaining a Jewish identity over the long term.