Starting Daf Yomi cycle - Berachot 2

One of the points I brought up in my Daf Yomi shiur today (Berachot 2) - the distinction between between siman and sibah. A siman is a sign, an easy way of knowing when something is (e.g. the terminus a quo of Shema). A sibah is a cause, the reason that the recital of Shema begins at that time.

The setama degemara takes the kohanim coming in to eat terumah as a siman. How so? Because really, it is tzeit hakochavim, and by tying it to the kohanim eating terumah, it teaches us something along the way (milta agav urcheih kamashma lan).

However, the brayta it excerpts from says "siman ladavar, tzeit hakochavim". It is the starts that is the siman. The implication, to me, is that the kohanim eating terumah is the sibah.

My favorite idea, one I keep returning to when I analyze midrash halachah and midrash aggada, is the hidden derasha. Sometimes Chazal don't make the derasha explicit, but a close reading of the pasuk and the halacha reveals an underlying derasha. I believe that this is the case for the many positions in the Mishna and Brayta on Berachot 2a.

בְּשִׁבְתְּךָ֤ בְּבֵיתֶ֙ךָ֙ וּבְלֶכְתְּךָ֣ בַדֶּ֔רֶךְ וּֽבְשָׁכְבְּךָ֖ וּבְקוּמֶֽךָ׃

Instead of beshivtecha beveitecha, read it as when you accept Shabbat in your house. Thus the position of when Shabbat is sanctified on erev Shabbat. See Iyov 30:17 and especially Kohelet 2:23 for shevet meaning rest from work, especially the poor laborer coming in from work. Thus, coming in from a long day at work and being at rest, during your meal, in your home (beveitecha) is the start time of recital. Rabbi Acha or Rabbi Achai speaks of hesieba, reclining, during a meal. Shochev has many meaning including merely lying down. Tying to a pauper or to a regular person has parallels to the time for recital of the morning Shema, either of a regular person or of a prince.

So it is not that recital was defined by the movements of heavenly bodies. Rather, it is defined by the movements of earthly bodies - the kohen, the regular person, the pauper. And there might be very fine differences in time when these things happen, and it doesn't need to fit into the rigid systematic slots the setama tried to wedge it into. And there are deep derashot at play, that people aren't realizing. And that is why each is a sibah, rather than a siman.