Question: But we learned in the Mishnah that such second thoughts do not remove the status of food from an item (and require that one act upon them in accordance with their new function to change their status)!?
Once a vessel is completed (via an act or a Machshavah), it can only change its status (and not be subject to Tum'ah), by an act, and not through Machshavah.
A Machshavah, however, cannot remove the effect of a prior act or a prior Machshavah!
Answer: We must differentiate between vessels and the stalks of fruit by saying that vessels (which are lasting and therefore significant) do not lose their finished status without an act, but not so fruit (which are only for eating, and therefore not significant) which could become subject to Tum'ah with a thought, and a thought is sufficient to remove that feature.
Question: But this will not fit according to R. Yochanan in the Mishnah regarding Besisah (to be explained)!?
R. Elazar explains the Mishnah in Uktzin (which declares Tahor the Yados of food she'Bisesan) to mean food whose bundles they untied.
We see, then, a form of removing susceptibility to Tum'ah through something less than an act (untying is not really an act, and is more comparable to a Machshavah).
R. Yochanan explains that Bisesan means threshing the corn (which destroys the Yados).
Then we see that even handles of food require an act to remove their eligibility to become Tamei (and how are we to understand the reason of Chachamim above)?
Answer: The Chachamim were also speaking where, when he decided to use the stalks for Sechach, he threshed them.
Question: Then why would Acherim argue!?
Answer: Acherim hold like R. Yosi who holds that even after Besisah, the stalks still retain their status of Yados.
Question: There is no comparison between the nullification of Yados of food and the Besisah associated with changing one's mind regarding Sechach!?
By Yados of food, R. Yosi holds like Resh Lakish, who holds that the Yados after threshing still have a function (one uses the stalks to turn over the tops of the wheat which are themselves too short to be held in a pitchfork).
But by Sechach, the Besisah should surely be a sufficient act to nullify the Yados, and what would be the rationale of Acherim to retain the Tum'ah of the Yados?
Answer: When he takes down the Sechach, the Yados will make it easier to collect it.
ANOTHER MISHNAH REGARDING BESISAH
(Tana Kama): Any Yados which had Besisah in the granary are not susceptible to Tum'ah.
(R. Yosi): They are still subject to Tum'ah.
Question: What is Besisah?
Answer (R. Yochanan): Actual threshing.
Answer (R. Elazar): Untying the bundle.
Question: While we understand R. Yosi's position if (as R. Elazar says) he only untied the bundle; but what would R. Yosi's rationale be if he actually threshed the Yados?
Answer (Resh Lakish): The Yados after threshing still have a function (to turn over the wheat which are too short for a pitchfork- Atar).
THE TEFILOS OF TZADIKIM ARE LIKENED TO AN ATAR
The Tefilah of a Tzadik is like a pitchfork (the word VaYe'tar is used in connection with Yitzchak's Tefilah) in that the Tefilah of a Tzadik, acts like a pitchfork, turning Hash-m's Din into Rachamim.
MISHNAH: PLANKS (NESARIM) AS SECHACH
(R. Yehudah): Planks may be used as Sechach.
(R. Meir): They are Asur.
A plank of four Tefachim invalidates the Sukah if it is in the middle of the Sukah, but not if it is adjacent to the wall of the Sukah.
One may not sleep underneath a four-Tefachim wide plank even if it is adjacent to the wall of the Sukah.
RAV AND SHMUEL INTERPRET R. YEHUDAH AND R. MEIR
(Rav): The Machlokes over planks is when they are four Tefachim wide.
R. Meir prohibits lest it be confused with a roof.
R. Yehudah does not have such a Gezeirah.
(Shmuel): The Machlokes is when the planks are less than four Tefachim (see Rashi) but four Tefachim is surely Pasul.
Question: Then anything, even reeds will be Pasul!?
Answer (R. Papa, interpreting Shmuel): Less than three is surely Kosher; more than four is surely Pasul, and the Machlokes is from three till four Tefachim.
R. Yehudah holds that less than the Shiur of a place (a Reshus, four Tefachim) is not subject to the Gezeirah (of being confused with a ceiling).
R. Meir holds that any area which could not be covered by Lavud (from three Tefachim) is subject to the Gezeirah.
Question: The Seifah of the Mishnah (which we assume is consistent with both R. Meir and R. Yehudah) is a question on Rav's interpretation of R. Yehudah!
The Seifah says that a four Tefachim board may be used (the Sukah is Kosher) but one may not sleep under it.
Shmuel understands why, according to all opinions, one may not sleep under a four Tefach board.
However, according to Rav, why should R. Yehudah prohibit sleeping under such a board?!
Answer: The Seifah is not all opinions (as we thought) but it is the opinion of R. Meir.
Question: The Beraisa is a question on Rav (first version).
(Tana Kama): Two cloths combine to four Tefachim of Sechach Pasul, but two planks do not.
(R. Meir): Planks are like cloth (presumably to combine to four Tefachim of Sechach Pasul to invalidate the Sukah).
Shmuel understands why two planks of three Tefachim would combine to invalidate the Sukah.
But when, according to Rav, would planks combine to invalidate a Sukah!?
A four Tefach plank invalidates without any need for combining it with another.
Planks of less than four Tefachim are fine (like reeds) no matter how many!
Answer: The planks in the Beraisa are four Tefachim wide, and we are speaking of combining to four Amos at the side of the Sukah (invalidating the Sukah because they are beyond the limits of Dofen Akumah).
Question: The Beraisa is a question on Rav (second version).
Shmuel understands that the combining of the Beraisa involves planks of three Tefachim combining to four Amos, and invalidating the Sukah.
Rav can understand R. Meir similarly with boards of four Tefachim (combining on the side of the Sukah to invalidate it).
However, R. Yehudah (who accepts boards of four Tefachim), why would the Mishnah say that they do not combine (implying that we accept that they are Pasul, but we reject the principle of combination)!?
Answer: The language (boards do not combine) used by the Tana Kama of the Beraisa is meant to parallel the language used by R. Meir (they combine), but not to imply that there is anything wrong with such four-Tefach boards.
There is a Beraisa to support each, Rav and Shmuel.
(In support of Rav): All agree that planks of less than four are Kosher, R. Meir holds that planks of four Tefachim are Pasul and R. Yehudah holds that they are Kosher. (R. Yehudah attempts to support himself there from an incident during a time of danger, a support which is disputed by the Chachamim).
(In support of Shmuel): Four Tefachim planks are surely Pasul, while planks of less than four Tefachim are permitted by R. Yehudah while R. Meir allows their use only if space equal to the size of the plank is left between the planks (R. Yehudah there allows a plank of four Tefachim at the side of the Sukah to be used, but not slept under).
TURNING THE PLANKS ON THEIR SIDES
(R. Huna): If planks four Tefachim wide but less than four Tefachim thick are placed on their sides, they still are Pasul.
(R. Chisda and Rabah. bar R. Huna): They are Kosher.
R. Nachman ruled that they are Pasul since they are like metal, meaning these boards bear the label of Sechach Pasul.
R. Huna asserted that this is how he had previously taught.
R. Chisda and Rabah bar R. Huna responded that R Huna had never provided a rationale, the way R. Nachman did.
R. Huna responded that they had never asked for a reason!
Question: Shall the following Beraisa be used in support of Rav Huna's rule (to invalidate the board on its side)?
After mentioning the Pesulim of a small Sukah and one with an opening at the bottom of the wall, the Beraisa invalidates a Sukah which has a plank that is four Tefachim wide, but which only takes up three Tefachim in the Sukah.
This appears to be the case of a four-Tefach board which has been turned on its side, giving us the Din of R. Huna!
Answer: No, the Beraisa is speaking of special Halachah called Pesel ha'Yotzei min haSukah.
A plank of four Tefachim is placed across the Sukah at the end where there is no wall, with three Tefachim within the line created by the opposite walls and one Tefach protruding beyond the Sukah line.
That additional Tefach is considered a legitimate part of the Sukah, and could be used as Sukah (Pesel ha'Yotzei - Sechach protruding onto an open side of the Sukah).
As such, the four-Tefach board invalidates the Sukah, since its entire area is considered part of the Sukah.