lannamichaels pointed out that Daf Yomi for Pesachim starts today and runs, conveniently, until just a few days before Pesach, inspiring me to try to pick it up again.
Daf 2The opening Mishna is about bedikas chametz, the hunting of and removal of leavened bread from one's house the day before Pesach starts. The Mishnah says that this happens during the אוֹר "Or", which is a word we usually translate as 'light'. This is strange. In actual fact of practice today, bedikas chametz is carried out the evening before Pesach, after dark. You hold up a candle and go around the house looking for chametz by candle light. Rav Huna wants to read אוֹר as 'light' and thus presumably some part of the day, but Rav Yehuda wants to read it as, somehow, meaning 'Evening'.
The Gemara therefore spends a while going through a lot of verses in Tanakh that use the word אוֹר and tries to understand their contextual meaning and see if אוֹר means Day or Evening. This is an additional strangeness! In this context, אוֹר appears in the Mishnah, not citing any particular Torah verse. It's a usage in Mishnaic Hebrew, so it's not straightforward to me why you would try to go back to Torah sources to understand its contextual meaning in the Mishnah.
I suspect there's more happening here than hermeneutics. The verses they explore involving light and darkness take us back to Genesis and the creation story, to various passages in the Psalms and Job, and I suspect that the Talmud is trying to bring these Torah contexts up because we're going to want to keep them in mind, to understand a lot more than just this question about bedikas chametz. The reason to explore this territory is because there is a lot in the Pesach story about questions of darkness and light. These are the fundamental questions of the observance of Pesach. There was a plague of darkness in Egypt, and the final plague Makat Bechorot happened in the dark as well. The Israelites left Israel under cover of night, and crossed the Sea of Reeds in morning's light, a process whose metaphoric significance appears all across the prayer service. Slavery to freedom is compared to a transition from darkness to light, so understanding how the Torah views light and darkness seems like a great way to start thinking about the laws of Pesach.
(There's also a sense I always get when studying the laws of Pesach in which the reenactment of Yetzias Mitzrayim extends beyond the Seder. The Rabbis are deeply concerned with exactly when all of these rituals must take place because they all have some equivalence to the events of Yetzias Mitzrayim and therefore the closer we are to the right times the closer our reenactment is to the original event.
Which is why we have two Seders in the diaspora)
In any case, this debate about bedikas chametz being in light or night leads us to a fascinating discussion of the categorical problem of Erev Pesach. Normally a holiday starts at sunset and runs until nightfall, and all the laws are applicable for the length of the holiday. But Erev Pesach has a bunch of ritual things that happen before Pesach starts, starting with bedikas chametz, which you could say is just pre-holiday cleaning. But more significantly, you stop eating chametz mid-morning on Erev Pesach. You offer the Korban Pesach in the afternoon of Erev Pesach. According to one position here and Rashi's explanation, some people even had the practice (minhag? chumra? unclear) of stopping doing melacha sometime in the morning of Erev Pesach. This is not usual, do we need to conceptualize Erev Pesach as a holiday itself? Maybe not, the Talmud cites minor fast days (Tenth of Tevet, Shiva Asar B'Tammuz, Tzom Gedaliah) as other examples of observances that only last part of a day. And I think that's a good way to think about the laws of Erev Pesach, too, probably. Since it involves Rabbinic extrapolations, you want to not observe them for a full sundown to sundown day in order to be clear that these are not additions to halacha.
But hm... Maybe I should have started with an introduction to Pesachim. Pesachim is the tractate of Talmud dealing with the observance of Pesach. It's not clear why the Rabbis called it Pesachim in plural. It may be because of Pesach Rishon in Nisan and Pesach Sheni in Iyar. The intro to Pesachim on Sefaria suggests thinking of Pesach Rishon instead as consisting of two holidays, one running from Erev Pesach through to first day of Pesach and involving the Korban Pesach, and the other running from the first night of Pesach for seven (or eight in Galut) days and involving the prohibition on chametz. The first 'holiday' is largely defunct because the Beis Hamikdash was destroyed; the second, with minor modification, is still practiced today.
This leads me into one of my major curiosities about how Pesachim is structured... In the Tannaitic period the Rabbis were reconstructing Pesach as a post-Beis Hamikdash observance by way of the Seder, and consistent with how the Talmud is composed there are two possible ways to create a Maseches Pesachim. One is to compose is as a historical record and reconstruction and imagining of the now inapplicable laws of the Beis Hamikdash on Pesach, as other Masechtas in Seder Kodashim tend to do. The other is to compose it as a guide to the new practice of Seder and the post-exilic idea of Pesach. I suspect it will be a combination, but I'm very fascinated to see how they struck the balance.
Now that I'm done being sidetracked, back to bedikas chametz! The first Mishna, once you get past its first word, is actually about when you DON'T have to do bedikas chametz. If you have a room in your house that you never bring chametz into, you don't need to search it. What if you have a room in your house that you don't typically bring chametz into, but you do bring food into it? The example in the Mishna is a cellar, apparently but not necessarily a wine cellar. (I kept thinking of
kass's 'root cellar' that she just built on her porch using a picnic cooler.) Here all agree that you have to do some searching but not that thoroughly. You can do some sort of spot check on the most well-trafficked sections and if they're clean, consider it chametz free. But Beis Hillel and Beis Shammai disagree about what the details of the spot check are. I'm sure the Gemara will get into more detail on their disagreement once it gets done looking at what אוֹר means, on future dapim.