How does the gemara know where to start?

Question

In any tractate, why isn't the background or explanatory information presented first?

For example, why do the laws of Shechita not begin with the laws of Shechita?

Masechet Chullin (and the Yoreh De'ah) begin the discussion of Shechita by listing those who are approved as shochets. In the gemara, a discussion of the actual details of the slaughter isn't until (unless I missed an earlier reference) daf 27 or so.

In an organized set of laws, wouldn't the foundational aspect -- the definition and the explanation of the topic, be more pressing than a list of who is eligible to perform the action?

In Megillah, the dates of the reading come first. In Brachos, the timing of saying Shma (and not establishing the obligation to say Shma) is first. Both Shabbat and Sukkah assume that one knows that there is an obligation to observe the holiday and the text jumps right in to detailed application of specific rules. [side note -- Kiddushin at least begins with the method but Ketubot, with the timing].

If the goal is to record a set of laws (and as they were oral, they could have been codified and written down in any order) why not set them up in a more logical sequence?

Answer 1

The Talmud is wont to ask this very question. So is Tosafot at the start of many tractates (See discussion in Bava Basra 2a among others). A few Talmudic examples which come to mind are: Taanit, Sotah, Shevuo etc. The basic formula observed is תנא מ- סליק, the Tanna has concluded the laws of X. Therefore, the Talmud argues that laws between one tractate and the next enjoy similarity. Although the Talmud could have began with the central theme, it prefers familiar territory. A great example is Taanit 2a:

אלא תנא מראש השנה סליק דתנן ובחג נידונין על המים ואיידי דתנא ובחג נידונין על המים תנא מאימתי מזכירין גבורות גשמים

The Teacher has just finished up talking about the previous tractate ‘Rosh Hashanah’ which concludes “and on this holiday we are judged for water”. So, since he was already discussing that topic, he moved on to teach the present chapter of “from when to we mention mighty rain”.

Notice that the first chapter of a four chapter compendium discussion of fasts does not begin with a discussion of fasts. I’d presume Yoreh Deah simply mimics the Talmud.

Answer 2

Here's my personal semi-metaphorical understanding of the problem. I asked this question a lot but I didn't find a Rabbi that deals with it so I propose my own (very allegorical though).

1. We compare the Torah to a tree as in Mishleh 3: "עֵץ חַיִּים הִיא לַמַּחֲזִיקִים בָּהּ וְתֹמְכֶיהָ מְאֻשָּׁר"

2. Ideally, a tree has roots, a stem, branches, smaller branches, and leaves. If we compare the Halochos to the leaves of the tree, we should have seen a clear path of reasoning from the roots of the Torah (probably hidden) through its stem and branches of Masechtos and Prakim, etc.

3. I speculate that this was the original form of the Oral Law - a complete tree.

4. Many Rabbis (see Rambam in Hil. Chidush Hachodesh, for example) mention that the Oral Torah was [almost] forgotten at some point after the destruction of the first Temple and the Sages of the Second Temple gathered the pieces of "left-overs" (Mishnayos) that were all parts of the Torah "tree crown" (think of a shrub), and not even its "branches".

5. Since then we only deal with that level and up, developing the Halochos further up, into new sub-branches, but we don't try to resolve how the existing pieces were related in the original tree of the oral Torah.

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Deep down I disagree with #3, that the Torah was once complete. It appears that for the Forefathers it was only in the form of roots, hence hidden, Moses got the stem (Matan Torah) and it was united and undivided and could contain all the Halochos that will eventually branch from it. Later in the 1st Temple they dealt with big branches of domains and when it arrived at the point when the Oral Torah was written (Midrash and Mishnah) it was already on the level of lesser branches, where the Mishnaic Rabbis didn't know/deal with the structure, only further developing.