How do we know this?

the long version

This book is a study of rabbinic legal interpretation (midrash) in Judaism's rabbinic, medieval, and modern periods. It shows how the rise of Reform, Conservative, and Orthodox Judaism in the modern period is tied to distinct attitudes toward the classical Jewish heritage, and specifically, toward rabbinic midrash halakah. What has gone unnoticed until now is the extent to which the fragmentation of modern Judaism is related to the interpretative foundations of classical Judaism. As this book demonstrates, spokespersons for any form of Judaism that engaged modernity on any level had to explain the basis for the rejection or continued acceptance of the authority of rabbinically developed law. Inevitably and invariably, this need led them to address anew what were long-standing questions regarding the ancient interpretations of biblical law. Were they compelling? Were they reasonable? Were they still relevant? Each form of Judaism fashioned its own response to these challenges, and each argued forcefully against the responses of the other denominations. . Jay M. Harris describes the fragmentation of modern Judaism in terms of each denomination's relationship to classical Judaism's system of interpretation in part two of this book.