Orach Chayim Siman 670:

Things that are Assur or Muttar on the Days of Chanukah

The development of: Se'if 1

CHANUKAH'S STATUS AS A "YOM TOV"*

The Gemara (Shabbos 21b⁴):

Question: What is [the origin of] Chanukah?

Baraisa (from Megillas Ta'anis¹): On the twenty-fifth of Kislev, the eight days of Chanukah [begin]. On these days, one may not eulogize, and one may not fast. [The institution of Chanukah, with this festive nature, resulted from the following:] When the Greeks ² went into the Beis HaMikdash³, they contaminated⁴ all of the oil there. [Later,] when the Hasmoneans⁵ overpowered and defeated the Greeks, they searched and found only one container of oil, which remained with the seal of the kohen gadol. There was only enough oil in it to light [the Menorah] for one day. [However,] a miracle was performed with it - and they lit [the Menorah] from it for eight days. In the following year, [the Sages of that generation (Rambam)] "established" those days - making them Yamim Tovim* with respect to "thanksgiving" and saying Hallel [but not as being assur in melacha* (Rashi⁶)].

Accordingly, the Shulchan Aruch starts the Se'if by ruling: On the twenty-fifth of Kislev ["begin" (Rema)] the eight days of Chanukah; and they are assur in eulogizing and in fasting, but they are muttar in melacha.

[The rest of Se'if 1 follows the next subject. In addition, more about eulogizing and fasting will be discussed in Se'if 3, and the Halachos of the above "thanksgiving and saying Hallel" are discussed in Siman 682 and Siman 683.]

1. The Sages established a number of holidays because of miracles which happened on certain days. They recorded the details in a work called "Megillas Ta'anis". Some of the holidays are listed there as "days that it's [only] assur to fast", and the others are described as "days that it's assur to eulogize [as well]". Subsequently, almost all of these holidays were cancelled, but Chanukah was not. (Ta'anis 15b [with Rashi], Rosh HaShanah 18b)
2. The Hebrew "Yevanim" is traditionally translated "Greeks". Whether or not the oppressors of the Jews at the time of the Chanukah miracle should be described as "Greeks" is beyond the scope of this project.
3. source's wording: "into the heichal". (The term "heichal" generally refers to the "main Sanctuary building" of the Beis HaMikdash.)
4. I.e. they caused the oil to become tamay [non-physically contaminated], and therefore it was no longer valid for the lighting of the Menorah. [As for how they caused this, see below.]
5. source's wording: "Hasmonean family leadership".
6. The Gra writes that in Megillah (5b) we see that this is a general rule: When Megillas Ta'anis says that a day is a Yom Tov, this does not mean to say that the day is assur in melacha.

* see Glossary º see Bibliography O.C. = volume Orach Chayim (of Shulchan Aruch, etc.)