Most of the time, Beit Shammai is of the strict opinion, while Beit Hillel is of the lenient opinion. The next two perakim (chapters) will talk about situations where Beit Hillel is more strict while Beit Shammai is lenient. The Mishnah says, “These are arguments between Beit Shammai and Beit Hillel where Beit Shammai is the lenient opinion and Beit Hillel is of the strict opinion.” The first case we’ll talk about is an egg that was laid on Yom Tov (holiday). This is the first Mishnah in Masechet Betza. Betza she'noldah b'Yom Tov, an egg that was laid on Yom Tov. Beit Shammai omrim te'achel and Beit Hillel omrim lo te'achel. They say, “Beit Shammai: You’re allowed to eat that egg on the day of Yom Tov,” and Beit Hillel says, “You’re not allowed to eat that egg.”
The reason behind this machloket—it’s a big dispute in the Gemara—but according to how we understand it, the Mishnah is talking about an egg that was laid on a Sunday. A Sunday that was Yom Tov, which follows Shabbat. We have a halacha (Jewish law) that all food that is prepared for Yom Tov is not allowed to be prepared from Shabbat for Yom Tov. An egg was prepared within the hen one day before Yom Tov, before it was laid automatically. So if it was laid on a Sunday, then it was prepared on the day before, which was Shabbat. So preparing for Yom Tov on Shabbat is a de'oraita (Torah-level) issue. And therefore, the hachana aspect of it, the fact that it was prepared improperly, says that we’re not allowed to gain benefit from that egg on Yom Tov. That is the opinion of Beit Hillel. And then Beit Hillel extends this and says, “Ah, there’s a problem of a Yom Tov that follows a Shabbat; we’re going to extend that prohibition to weekdays as well.” Because if you allow a person to eat an egg that was laid on a regular Yom Tov that was on a weekday that did not follow Shabbat, then they may also eat it on a Sunday as well, which is a violation of the Torah. That was the concern of Beit Hillel.
But Beit Shammai ruled leniently. They never learned out this whole idea of hachana, that things are not allowed to be prepared from Shabbat to Yom Tov. They didn’t learn out from these pesukim (verses). So therefore, they allowed an egg that was laid on Yom Tov to be consumed.
The next machloket we’ll have is about Pesach. On Pesach, a person is not allowed to own or eat chametz (leavened food). He’s also not allowed to own or eat sourdough, which is a dough that has fermented and has the ability to cause other dough to rise. So we’ll have a machloket in Beit Shammai, Beit Hillel, about the minimum amount of these items that a person is not allowed to eat. So we’ll have a machloket in Beit Shammai, Beit Hillel, about the minimum amount of these items that a person is not allowed to own or eat on Pesach. Beit Shammai omrim se'or b'kezayit v'chametz b'kakotevet. They say, “Beit Shammai, the smallest amount of sourdough that the Torah says is a problem for you to own or eat on Pesach is an olive size. But when it comes to chametz, when it comes to regular chametz, as opposed to sourdough, the Torah prohibits only a date volume and more.”
A date is larger than an olive. So according to Beit Shammai, if a person owned an olive size, for example, he would not be violating the Torah. That’s the opinion of Beit Shammai: to violate with se'or, with sourdough, even a small amount of a kezayit brings on the violation of the Torah. But when it comes to regular chametz, only a larger amount of a kakotevet, a date, is how a person violates. According to Beit Shammai, sourdough is something we’re more mahmir with because it’s different. It’s different than chametz because it’s stronger. It can cause chametz to rise. So therefore, even with an olive size, a person has violated the Torah. Or Beit Hillel, no, this and that, sourdough and chametz, both of them, if a person owns them at the size of a kezayit, then they have violated the Torah and they’re equal in their prohibition.