Baba Basra 119b - Honoring a Student in the Presence of His Rebbi

The gemara says that one is not required to honor his rebbi even in the presence of his rebbi's rebbi, unless the rebbi's rebbi went out of his way to show honor to the rebbi indicating that he wants you to honor him. Presumably the rationale is that to honor a student in the presence of his rebbi, even if that student is your rebbi, is considered a lack of kavod for the rebbi, therefore, it is only permitted if the rebbi is mo'chel on his kavod and allows you to show honor to his student in his presence. The Shulchan Aruch (Y.D. 242:21) paskens this. One shouldn't stand up for their rebbi in the presence of his rebbi or stand up for his father in the presence of the father's rebbi, unless the rebbi indicates that he allows the honor shown to his student. However, the Rama qualifies this to cases where the student of the rebbi is also a student of the rebbi's rebbi, but if the student is only a student of his own rebbi and has no connection to the rebbi's rebbi, he isn't required to show kavod to the rebbi's rebbi by not honoring his rebbi in the presence of the rebbi's rebbi.

But, the Shach (40) quotes the Mahar"i HaKohen from krakow (maharik) who argues and holds that even if the student never learned anything from his rebbi's rebbi, he is obligated to honor him and show more kavod to the rebbi's rebbi than to the rebbi. And if he even learned a little from the rebbi's rebbi then he cannot show kavod to his rebbi in the presence of the rebbi's rebbi (unless he is mo'chel).

The nachalas tzvi explains that the source for the Maharik that one is required to honor his rebbi's rebbi even if he hasn't learned anything from him, is the gemara in kiddushin that says that the kavod of a father preceeds a mother (assuming they are married) because she is also obligated in the kavod of the father. Similarly, the student should show more kavod to the rebbi's rebbi than to the rebbi, since the rebbi himself is obligated in the kavod of his rebbi. But, the difficulty with this concept is that we hold that the kavod to a father supersedes the kavod to a grandfather (shulchan aruch 240:24) - why don't we say that the grandson owes more honor to his father's father, since his father is also obligated to honor him? This question is the key point in determining our halacha. If we assume that a grandson is obligated to honor a grandfather, as the rama writes (240:24), then we see that even though the son is obligated to honor his grandfather, and the father is obligated to honor the grandfather, the honor to a father would still come first. Therefore, the rama goes li'shitaso that the honor shown to a rebbi would supersede the honor to a rebbi's rebbi, and you don't need permission to honor the rebbi (unless you are also his student). But the maharik must hold that there is no real mitzvah to honor a grandfather, and therefore would hold that we can't compare our case to a father and grandfather, because here there is still a mitzvah on the talmid to honor the rebbi's rebbi as a chacham. Therefore, even if the student has not learned anything from the rebbi's rebbi, he is still obligated to honor him more than his rebbi.

The underlying issue is whether the requirement of the rebbi to honor his rebbi, would also require the student to honor his rebbi's rebbi even more than his rebbi, or do we only require the student to honor the rebbi's rebbi more than his rebbi when he has a direct connection to him because he actually learned from the rebbi's rebbi also.