That the existence of a separate, recalcitrant, and even obnoxious nation within a nation did not constitute a problem for the medievals may be attributable to two reasons: (1) the medieval theory of life accentuated a hierarchical order of existence--a theory that found expression in feudalism, in Church organization, and in guild and craft life; in pursuance of this theory, the Jews were accorded a recognized and distinct status; (2) furthermore, the Jews were an economic necessity in the times when a ban was laid on money-lending, and they constituted an important economic facility at a little later period when capital could indeed be worked but when rivalry and hatreds rendered communication uncertain.[6] To the maintenance of Jewish solidarity and the preservation of things Jewish _qua_ Jewish, sacrifices culminating in the surrender of life bequeathed to the race a comprehensive martyrology.[7] Ernest Renan defines a nation as "a great solidarity constituted by the sentiment of the sacrifices that its citizens have made and those they feel prepared to make once more. It implies a past, but is summed up in the present by a tangible fact--the clearly expressed desire to live a common life." In sum, the Jews throughout the Middle Ages, which was prolonged for them until a little less than two hundred years ago, comprised a nation as virtual in point of their own claim and its recognition by other nations as in the days when they were established in Palestine. Renaissance, Reformation, and the rediscovery of the world by science failed to make an impression on the thick ghetto walls; and Jewish isolation, even as late as the eighteenth century, may be vividly realized by thinking of Rousseau and Voltaire in contrast with the contemporary lights of Jewry--Elijah Gaon and Israel Besht,[8] men as medieval as a gargoyle. The French Revolution with its early philosophy of naturalism and humanism and its later political expression in liberty, equality, and fraternity, razed the physical and spiritual walls of the ghetto and set up the "Jewish problem." Following the Revolution, four currents of thought and action, working both simultaneously and successively, causing, reacting upon, and intermingling with one another, affecting the Jews now favorably and now unfavorably, went into the making of this problem. To deal with Emancipation, Enlightenment, Nationalism, and Anti-Semitism in detail would consume a volume, but an outline of their bearing on the present situation is essential. _Emancipation and Enlightenment_