Abaye writes that besides the verse "Shiv'as Yamim Se'or Lo Yimatzei," which prohibits Chametz during the seven days of Pesach, there is an additional verse, "Ach ba'Yom ha'Rishon," which includes the fourteenth of Nisan in the prohibition of Chametz.

Rashi offers two explanations for how Abaye understands the second verse. The first is that since the verse says that we must do away with the Chametz on the fourteenth day, it is clear that at the beginning of the day it is still permissable. The second explanation is that the word "Ach" can be converted to the word "Chetz" using a method of alphabetic transposition, and therefore "Ach" means half, i.e. half a day.

Tosfos learns that the law of Abaye is derived merely from the fact that the second verse is an extra verse.

D. Zupnik