Of all the Jewish thinkers that arose in the twentieth century, none stands out as revolutionary and as controversial as Mordecai Kaplan. Kaplan was paradoxical to say the least. He maintained high levels of personal religious observance and in addition to his studies at the Jewish Theological Seminary he also obtained traditional ordination. He served as an Orthodox rabbi for a short duration and was also participated in the founding of the Young Israel movement.
For Kaplan Orthodox, Reform, and Conservative Judaisms are based upon the view that the key differences between Jews and non-Jews lie solely in the area of religious thought. For the aforementioned versions, the challenge of Jewish life in light of modernity is the appropriate adaption of Jewish beliefs and practices -even as was noted in the case of Neo-Orthodoxy.
For Kaplan the challenge of Jewish life in the twentieth century was based on far more than the issue of Jewish religion. For Kaplan, Jewish faith is only one element in the life of a Jew that is challenged by modernity. Yet despite his commitment to Jewish life as recognizable to traditionally oriented Jews, his theological predilections were such that the fundamental nature of Jewish theological identity was transformed in his reconstruction of Judaism. His work "Judaism as as Civilization and The Meaning of God in Modern Jewish Religion" and the philosophy behind them highlight very different notions of God, Torah, and Israel when compared to classical Jewish perspectives. Yet while Kaplan was vilified by many Orthodox and finally excommunicated by the rabbis of Agudath Israel, not all his right of center critics were ready to completely dismiss if not the motivation behind Kaplan's restructuring or reconstruction of Judaism, the very issues he addressed
In his quest to define what Judaism is, Kaplan took issue with all the movements existent in his day. While acknowledging the "success" of the Reform movement if in nothing else, preventing the flow of thousands of Jews in Western Europe and in the United States from abandoning Jewish identity, Kaplan saw Reform Judaism as espousing a religious philosophy devoid of the meaning of the Jewish people and its distinctive culture. Kaplan argued that Judaism reflected "Jewish consciousness"; Judaism was the "heart of the Jewish people."
For Kaplan then, a Judaism based solely on the idea of ethical monotheism was unsustainable. Reform Judaism was asking religious Jews to be the emissaries of what was a religious philosophy. Furthermore the great thinkers of Reform Judaism assumed that Jews had always embraced theological ideas that were advanced beyond that of other nations. Having rejected a supernatural revelation as the source of this claim, Kaplan saw inherent weakness in any attempt to appeal to history as the arbiter of such a view.