Since Shmuel is oser one type of kavla de'avda and is matir another type, why doesn't the Gemara just make an ookimta in the mishna that the Mishna speaks about the type that Shmuel is oser and therefore Shmuel can be matir the other type?
Martin Taubman, England
Your question is asked by Tosfos 58a DH ve'ha'Omar. Shmuel (58a) stated that he agreed with the interpretation that the prohibited "Kvul" of the Mishna is "Kavla de'Avda".The Gemara posed a contradiction in Shmuel's position because in another statement Shmuel says that the slave may go out with the seal around his neck (Rashi writes that this is identical to Kavla de'Avda) but may not go out with a seal on his clothing. Tosfos asks why one could not explain that the Kvul of the Mishnah is the seal on the clothing and is therefore forbidden, whilst the seal round his neck is permitted. Tosfos answers that the Gemara prefers to understand that the Mishnah refers to all kinds of seals, either on his neck or on his clothing, and to say that the Mishnah only prohibits the seal which the slave himself made.
Kol Tuv,
D Bloom