in D'H me'masai. R.Tam says we can say shema by plag because of R Yehuda says mariv at that time. But shema is governed by b'shochbecha(when you lie down) not by when night begins. every knows people dont ly down at that time. even R. Yonah say you can't but the berchos to shema can bec. it night time for berchos of shema but not shema itself bec governed by (WHEN YOU LIE DOWN)
AND the Riy on that tosfos brings proof from rebbi saying shema early on erev shabbos.thats bec of marriv and maybe repeated shema after 3 stars and R Tam says night begins 72MINUTES AFTER SUNSET so how can he say mariv and shema what is the reason for both.
And why do we make a gezrah for shema at night and not in the morning lest one over sleeps in the morning
Ronnie Ben-Ishay, Forest Hills
Your first two questions -- "Z'man Shechivah" and what was the Ra'ayah from Rebbi -- are the Rosh's questions on Tosfos. According to Rebbi Yehudah, Maariv starts after Minchah, not at three stars.
I don't understand how your proposed Gezeirah would help. At night we want the person to say Shema early and not get involved in something that might make him miss Shema, but if the person oversleeps he is going to be worse off with a Gezeirah.
D. Zupnik