The first systematic and critical academic proof for the authorship of Moses de León was given by Adolf Jellinek in his 1851 monograph "Moses ben Shem-tob de León und sein Verhältnis zum Sohar" and later adopted by the historian Heinrich Graetz in his "History of the Jews", vol. 7. The young kabbalah scholar Gershom Scholem began his career at the Hebrew University in Jerusalem with a famous lecture in which he promised to refute Graetz and Jellinek, but after years of strained research Gershom Scholem contended in 1941 that de León himself was the most likely author of the Zohar. Among other things, Scholem noticed the Zohar's frequent errors in Aramaic grammar, its suspicious traces of Spanish words and sentence patterns, and its lack of knowledge of the land of Israel.