Yoma 3,Thoughts on the Daily Daf, regarding argument between Rebbi Yochanan and Rebbi Yishmael:
In the 2nd para to the Question (on page 1) it is written, "...Rebbi Yochanan,
unlike Rav was a full-[fledged Amora and cannot argue with a Tana."
(a) My Question: Is there a cut-off point in time particularly when a scholar could
not be identified with a Tana. Or has time nothing to do with it, but rather the
level of learning and clear conception pertaining to all matters of Torah learning?
In other words, what defines a Tana as such or an Amora as such?
(b) Additional Question: When two scholars are mentioned in the gemorah, one stating
a rule in the name of his teacher or predecessor, which name (assuming one
wishes to mention only one for expediency) should one quote in authenticating the
rule or dictum: the original sayer, or the quoter (or student)?
Best regards and wishing Rabbi Kornfeld and the rest of the Kollel members a
frelechen Purim.
(a) Generally it is the time in which a sage lived which defines whether he was an Amora or a Tana, but in a deeper sense that reflects how knowledgeable he was. In other words, if a sage lived in the times of the Beis ha'Mikdash, for example (Tannaic times), he was on a much greater level of scholarship than a sage living a few hundred years after the Churban.
The sages who lived in the generation immediately following the time when the Mishnah was redacted, such as the students of Rabeinu ha'Kodesh, the status of those sages is in doubt whether they are considered Tana'im or Amora'im. Therefore, it could be determined based upon their scholarship (and experience and interaction with the Tana'im) whether they could be considered a "Tana Hu u'Palig," such as Rav, or could not be considered to have the status of a Tana, such as Shmuel and Rebbi Yochanan. Even though they were colleagues of Rav and we find that they in fact argued with Rav, nevertheless Tosfos says that they maintained that Rav is not considered a Tana.
In the generation after those sages, however, everyone was considered an Amora and we find no doubt about this. It was not possible, either, to excel so much in scholarship and righeousness that one "achieved" a level of a Tana, because the particular place on the timeline of history at which the Tana'im lived -- that is, closer to the original Revelation at Sinai and more connected to the transmission of the Oral Torah -- defined their status as Tana'im, and thus by definition anyone who lived later could not be a Tana.
(b) When there is an argument about what the teacher said (for example, Rav Kahana says that Rav said one thing, and Rav Asi says that Rav said something else (cf. Shavuos 26a)), then of course both names need to be mentioned. When no one argues what the teacher said, then it suffices to mention the name of the teacher.