given passage. Further variant readings can often be gleaned from citations in secondary literature such as commentaries, in particular, those of Alfasi, Rabbenu Ḥananel and Aghmati, and sometimes the later Spanish commentators such as Nachmanides and Solomon ben Adret. Historical analysis, and higher textual criticism Historical study of the Talmud can be used to investigate a variety of concerns. One can ask questions such as: Do a given section's sources date from its editor's lifetime? To what extent does a section have earlier or later sources? Are Talmudic disputes distinguishable along theological or communal lines? In what ways do different sections derive from different schools of thought within early Judaism? Can these early sources be identified, and if so, how? Investigation of questions such as these are known as higher textual criticism. (The term "criticism" is a technical term denoting academic study.) Religious scholars still debate the precise method by which the text of the Talmuds reached their final form. Many believe that the text was continuously smoothed over by the savoraim. In the 1870s and 1880s, rabbi Raphael Natan Nata Rabbinovitz engaged in the historical study of Talmud Bavli in his Diqduqei Soferim. Since then many Orthodox rabbis have approved of his work, including Rabbis Shlomo Kluger, Joseph Saul Nathansohn, Jacob Ettlinger, Isaac Elhanan Spektor and Shimon Sofer. During the early 19th century, leaders of the newly evolving Reform movement, such as Abraham Geiger and Samuel Holdheim, subjected the Talmud to severe scrutiny as part of an effort to break with traditional rabbinic Judaism. They insisted that the Talmud was entirely a work of evolution and development. This view was rejected as both academically incorrect, and religiously incorrect, by those who would become known as the Orthodox movement. Some Orthodox leaders such as Moses Sofer (the Chatam Sofer) became exquisitely sensitive to any change and rejected modern critical methods of Talmud study. Some rabbis advocated a view of Talmudic study that they held to be in-between the Reformers and the Orthodox; these were the adherents of positive-historical Judaism, notably Nachman Krochmal and Zecharias Frankel. They described the Oral Torah as the result of a historical and exegetical process, emerging over time, through the application of authorized exegetical techniques, and more importantly, the subjective dispositions and personalities and current historical conditions, by learned sages. This was later developed more fully in the five-volume work Dor Dor ve-Dorshav by Isaac Hirsch