- Peninei Halakha
The fifth of Iyar can fall out on a Monday, Wednesday, Friday, or Shabbat. When it falls out on a Friday or Shabbat, there is good reason for concern that the celebrations and ceremonies will cause public desecration of Shabbat. Therefore, it was decided – at the request of the Chief Rabbinate – that whenever the fifth of Iyar falls out on a Friday or Shabbat, Yom Ha-atzma’ut is celebrated on the preceding Thursday (the third or fourth of Iyar). Eventually, it became apparent that even when Yom Ha-atzma’ut falls out on a Monday, this still causes Shabbat desecration. Since Yom Ha-zikaron (Memorial Day), which takes place the day before Yom Ha-atzma’ut, begins on Saturday night in this case, this causes many Jews to desecrate Shabbat in preparing for Yom Ha-zikaron. Therefore, it was decided – again at the request of the Chief Rabbinate – that both of these holidays would be postponed by a day, such that Yom Ha-zikaron would be observed on the fifth of Iyar and Yom Ha-atzma’ut on the sixth of Iyar. In practice, then, on three of the four days on which Yom Ha-atzma’ut can potentially fall, we celebrate it either before or after its genuine date.
We find a similar concept in the laws of other holidays. Out of concern that one might carry a shofar or lulav through reshut ha-rabim (the public domain) on Shabbat, the Sages canceled these mitzvot on Shabbat. Therefore, when Rosh Ha-shana falls out on Shabbat, we do not blow the shofar that day, and when the first day of Sukkot falls out on Shabbat, we do not take the lulav that day. Thus, the Sages canceled Torah commandments in order to avoid Shabbat desecration. Despite this, we may not change the actual date of a holiday since it is written explicitly in the Torah. The date of a rabbinically ordained holiday, however, may be moved. For example, when Purim falls out on Shabbat, we read the megilla and give gifts to the poor on Friday, read the special Torah reading and recite Al Ha-nisim on Shabbat, and eat a festive meal and send mishlo’aĥ manot to others on Sunday (sa 688:6, mb ad loc. 18; below 17:5). And when Tisha Be-Av falls out on Shabbat, we postpone the fast until Sunday (see sa 551:4, 554:19).
The same is true of Yom Ha-atzma’ut; it all depends on how the holiday was instituted. Whichever day the representatives of the people and the Chief Rabbinate decide is the day to celebrate the establishment of the State is the day when we must thank God for His salvation.
It is interesting to note that the actual declaration of Israel’s independence took place earlier than originally planned, in order to prevent Shabbat desecration. The British Mandate ended on Friday night at midnight, but the heads of the People’s Council did not want to declare statehood through Shabbat desecration, so they moved the declaration up to Friday afternoon, the fifth of Iyar.
 This has been the Chief Rabbinate’s position throughout its history. It is true that, in 1981, R. Shlomo Goren believed that one should recite Hallel on the fifth of Iyar when it falls out on Shabbat, reasoning that whatever festive practices do not entail Shabbat desecration should be observed in their proper time, as is the case on Purim (Torat Ha-Shabbat Ve-hamo’ed). Nevertheless, all the other rabbis maintained that no distinction should be made, as R. Yaakov Ariel explains in Be-ohalah shel Torah §73. R. Ariel states that it seems we should omit Taĥanun on the fifth of Iyar (if it falls on a Friday), just as Tisha Be-Av retains its status with regard to certain laws even when it falls out on Shabbat (ibid.). He concludes that if the fifth of Iyar falls out on Shabbat, we still recite Av Ha-raĥamim, because of the misfortunes that occurred in Iyar. It seems to me that we should, nevertheless, omit Tzidkatekha from the Minĥa service. It also seems – and so decided the Chief Rabbinate in 2004 – that when the fifth of Iyar falls on a Monday, meaning that Yom Ha-atzma’ut is pushed off to Tuesday, we do not recite Taĥanun on Monday. In his work Ha-Rabbanut Ha-Rashit (pp. 898-899), R. Shmuel Katz explains that even R. Goren originally maintained that Hallel should be recited on the day that was chosen for the general celebrations, as opposed to Shabbat. He changed his mind only later, in 1981. In n. 33, R. Katz relates, in the name of R. Yitzĥak Alfasi, that in 2001 the members of R. Goren’s synagogue, Komemiyut Avraham, followed the prevalent custom not to recite Hallel on Shabbat, because some heard from R. Goren that the general public did not accept his ruling on this matter.
Rav Kook writes in Mitzvat Re’iyah, oĥ 688:1 that the Sages instituted two days of Purim in order to distinguish between a Torah commandment, which has one fixed time for everyone, and a rabbinic commandment, which is observed at different times in different locations. Perhaps this explains why the Sages instituted two levels of mehadrin observance with regard to lighting Ĥanuka candles, a feature that is not found in relation to Torah commandments, whose laws are fixed. Based on this, we can state that it is fitting for Yom Ha-atzma’ut not to have a fixed date, seeing that it is a rabbinic enactment.