Pesachim 3: The Gemara finally asks - why didn't the mishnah just say "night"?? Using the positive version of negative words (tahor (pure) and eino tahor (not pure), instead of tameh (impure - admittedly, this distinction is less strong in English). The agenda, though, is clearly to speak always in a refined manner. So what then IS refined speech, especially given how the bar moves in society... But then the Gemara also prioritizes brevity. So refined language can trip you up, and the Gemara is aware of that. Rav lived up to the refined language concern, however, when he refused to speak to students whose speech was rough. But maybe Rav was in a different class.... Plus: The concern that we don't look into the lineage of the priests to check if they are legitimate is countered by a powerful story where checking into the background of a particular schemer would have been better (don't worry, R. Yehudah ben Beteirah saved the day). But note that the lineage concerns of kohanim goes back a long time... (See Editor too).