Critical Notes on al-Fāsī
Al-Fāsī
Abbaye said: We have a tradition that if no priest is there, the package is separated [i.e., the order of Torah readers no longer has to be a priest, then a Levite, then Israelites].
Rashbam
I, Samuel, heard that this means only that the fixed order may be separated, but a Levite may read like an Israelite.
However, there have been great disputes in Ashkenaz over this, as some explain that a Levite may not read the Torah at all since no priest is available to be the first reader. They cite a proof from a passage: “I presume that this individual is a priest. What is the proof? That a Levite reads after him” [b. Ketubbot 25b]. This implies that a Levite may read only when he follows a priest. However, this is not a decisive proof, as it might be said that there were other priests in that synagogue, and if that man [who was reading] had read in the place of the priests [despite not being a priest] due to his great stature, a Levite would not have read after him [instead, a priest would have read next], since other priests were present.
Published in: The Posen Library of Jewish Culture and Civilization, vol. 3: Encountering Christianity and Islam.