One does not need to have the authentic Hittite nose to be a Jew; the term Jew rather denotes a special way of thinking and feeling. A man can very soon become a Jew without being an Israelite; often it needs only to have frequent intercourse with Jews, to read Jewish newspapers, to accustom himself to Jewish philosophy, literature and art. On the other hand, it is senseless to call an Israelite a 'Jew', though his descent is beyond question, if he has succeeded in throwing off the fetters of Ezra and Nehemiah, and if the law of Moses has no place in his brain, and contempt of others no place in his heart.
The Foundations of the Nineteenth Century (Die Grundlagen des neunzehnten Jahrhunderts) (1899)