what does it mean dichiah by yom tov
yehoshua rabinowitz, beverly hills, l.a.
The following is what we wrote in the Background section to that Daf.
6) [line 12] YESH DICHUY ETZEL MITZVOS (once a Mitzvah is suspended it is forever suspended)
(a) The concept of Dichuy applies to many Halachos in the Torah where a certain object is required for a Mitzvah or Korban. Some examples are limbs and blood of the Korbanos, blood of Kosher birds and wild animals that must be covered with dirt, live animals for Korbanos and objects used to perform Mitzvos.
(b) The question of Dichuy with regard to objects used to perform Mitzvos applies in two instances: 1. the object was only fit for use after the time that the Mitzvah first applied ("Dichuy me'Ikara"); and 2. the object was fit for use at the time that the Mitzvah first applied, later became unfit, and afterwards became fit again ("Nir'eh v'Nidcheh"). In the latter case the Dichuy is stronger.
(c) At this stage of the Gemara, Rebbi Yirmeyah ponders whether or not we rule that once an object is unfit for a Mitzvah (Dichuy me'Ikara) it is forever suspended from being used for that Mitzvah. For example, the Hadas was unfit for use on Erev Yom Tov because of Niktam Rosho. On Yom Tov, an excretion in the shape of a date grew on the Hadas, covering the Rosh Katum. Is the Hadas now fit for use or not?
Kollel Iyun Hadaf