The problem: Whenever Shabbos immediately follows Yom Tov, we are faced with the following challenge: When are we going to cook for Shabbos? We understand that we may cook on Yom Tov for itself, but may we cook on Yom Tov for Shabbos, which is the next day? (Obviously, we may not cook on Shabbos!) Indeed, we are commanded to eat well on this Shabbos, as on every other Shabbos, but how can we practically accomplish this in a halachically-permitted manner? One solution would be to eat Yom Tov leftovers! This is a serious option. In fact, we may even plan on having plenty of leftovers by cooking more on Yom Tov than we know we will need, so that much will still remain for Shabbos! In order to understand the parameters of this option, it would be necessary to review the halachos of the ‘heter’ (permit) of ‘marbeh b’shiurim’ (making larger quantities), which are found in detail in the lesson MBY 503:1-2 Preparing food on Yom Tov for the next day.
In the lesson on siman 503, we foretold another method for preparing for Shabbos which would be discussed in siman 527 (We’re here!) through the use of the Eruv Tavshilin. Essentially, this means beginning the cooking of our Shabbos food before the Yom Tov even begins. Once we have begun, it now becomes permissible to continue cooking on Friday for the sake of Shabbos, even though Friday is Yom Tov (either 1st or 2nd day.)
Before we get into the details of how to make the Eruv Tavshilin, let us take a few minutes to discover why it was instituted by the Rabbis, and how it works to permit that which is otherwise forbidden, i.e. cooking on Yom Tov for Shabbos. A correct understanding of any halachic system requires a discerning mind to recognize the difference between a Torah law and a Rabbinic law. Basically, the Rabbis can create a ‘heter’ (permit) only to do that which they prohibited in the first place. They cannot create a ‘heter’ to do that which the Torah prohibited. [Ed: Compare this to the ‘Eruv’ which permits carrying on Shabbos. Did you know that the ‘Eruv’ - created by the Rabbis - permits carrying in a ‘karmelis’ (sub-public domain, such as a side street) only - not in a ‘reshus harabim’ (major thorough-fare)? The reason is because the Torah prohibits carrying in a ‘reshus harabim’; the Rabbis extended that prohibition to the ‘karmelis’. The Rabbis’ Eruv can permit carrying only in the areas which they prohibited – not in the areas prohibited by the Torah!]
If you are game to learn, I am game to teach. Ready?!
Step 1: What does the Torah say about cooking on Yom Tov for Shabbos?
We wondered above whether or not we may cook on Yom Tov for Shabbos. Why or why not? We know that we may not cook on Yom Tov for a weekday, because the Torah allows us to cook only that which we need for our food that day. [Remember Shmos 12:16: “On the first day shall be a holy convocation, and on the seventh day shall be a holy convocation for you, no work may be done on them, except for what must be eaten for any person – only that may be done for you.”] The verse clearly refers to food which must be eaten on Yom Tov itself, not on the day after Yom Tov, right? After all, it is not necessary to cook on Yom Tov for the next day, because you can cook then! [We also know that the Torah is not permitting us to cook on day 1 of Yom Tov for day 2 of Yom Tov, because… (think hard now!) …there is no such thing as a two-day Yom Tov according to the Torah!] Clearly, whatever melacha is not expressly permitted on Yom Tov is strictly prohibited by the Torah, right? But what does the Torah say about cooking on Yom Tov for the next day when the next day is Shabbos? For one, we don’t the option of cooking on Shabbos for itself. For another, this is a unique situation where two Torah-based holy days come back-to-back. Perhaps since Shabbos and Yom Tov are both holy, the Torah permits cooking on one day for the next, just like it permits cooking on Yom Tov for itself. See?
The answer is YES – the Torah permits cooking on Yom Tov for Shabbos; however, there are two divergent opinions as to the reason why: One opinion (held by Rav Chisda in Pesachim 47b) is straightforward that Shabbos cooking may be done on Yom Tov, for the reasons stated above. The other opinion (held by Rabah) is that in principle, Shabbos cooking may not be done on Yom Tov; however by an entirely separate rationale, the Torah would permit it under certain conditions. The rationale is known as the ‘ho-il’ principle. Ho-il (lit. “since”) states that “since” something is hypothetically possible, we can consider it reality. (Now don’t get carried away by the sound of this principle, hear?!) The application here is as follows: Suppose it is Yom Tov afternoon and we have already eaten the daytime meal. If guests would suddenly arrive to my home without having eaten a meal yet today, would I be permitted to cook for them? Of course! Well, “since” I could cook were the guests to come, I may cook now even if they have not come! There is a caveat, however, according to Rabah and the ho-il principle: One may only cook until a time in the day at which it would be reasonable for him to still cook for guests were they to arrive. If it’s already late in the day, one would not have the time to begin preparing a meal and serving it to his guests. At that point, then, there would indeed be a Torah-prohibition to cook anymore. See the difference?
[Step 1 Summary: Cooking on Yom Tov for Shabbos is permissible according to the Torah by all opinions – either because the Torah permits it straightaway (Rav Chisda), or because of the ho-il principle (Rabah). According to Rav Chisda, one may cook until the last minute of the day (i.e. before sundown). According to Rabah, who relies on the ho-il principle, one may not cook late in the day.]
Step 2: What do the Rabbis say about cooking on Yom Tov for Shabbos?
Although the Torah permits it (for one of the two reasons stated above), the Rabbis did not approve un-mitigated cooking on Yom Tov for the next day Shabbos. They had two concerns (See Beitzah 15b): 1) People might neglect to prepare respectable meals for Shabbos, turning all of their attention (and expenditures) to the first - and more “eventful” - Yom Tov meals. It is quite possible that the Shabbos preparations would be made almost as an after-thought, and little good food would remain in the household for the Shabbos meals. 2) People may come to err in the halacha: One year they will prepare on Yom Tov for the next day (because it is Shabbos); the next year they may think to do the same, even though the next day is not Shabbos but a weekday (which the Torah definitely does not permit!) In order to rectify these concerns, while still allowing for Shabbos preparation on Yom Tov, the Rabbis instituted Eruv Tavshilin. “Begin Shabbos preprations early – before Yom Tov even starts!” they ordained. “Make one cooked dish and one baked food for Shabbos.” In so doing, the two concerns are rectified: Concern #1) We will not be guilty of neglecting Shabbos in favor of Yom Tov, because we will have already set aside some good Shabbos food before Yom Tov begins; and Concern #2) We will be reminded that it’s only on a year like this one, when Shabbos follows Yom Tov, that we are allowed to cook on Yom Tov for the next day – not on a regular year!
[Step 2 Summary: How does Eruv Tavshilin permit cooking on Yom Tov for Shabbos? First of all, the Torah permits it! The Rabbis are the ones who did not want to permit it. However, those same Rabbis ordained that if we make the Eruv Tavshilin, they will permit it as well, for in so doing, their concerns are rectified.]