On daf 4a the gemorah says that Dovid Hamelech needed the Harp to wake him up at chatzos. My question is that on the previous Amud the gemorah brings Rav Ashi who says that Dovid Hamelech learnt from evening to chatzos. If Dovid Hamelch learnt till chatzos, then why did he need the harp to wake him up?
dov neuhaus, brooklyn, ny
The Gemara gives two reasons for David Hamelech's harp; 1. to inform him exactly when it was midnight, and 2. to arouse him from his shallow sleep.
You perhaps did not notice that Rebbi Zeira, who adopts the latter view, is the one who learned above that David slept until midnight. Rav Ashi, who takes on that he awoke long before midnight, will no doubt learn like Rav Yitzchak bar Ada, that the purpose of the harp was to ascertain when midnight arrived (and not to wake him up).