## Tosafot on Bava Batra Daf 4b

###### Tosafot on Bava Batra 4b:2:1
[Tosafot on Bava Batra 4b:2:1](https://torahapp.org/share/book/Tosafot%20on%20Bava%20Batra/r/4b:2:1)

גייז ליה חבריה ושדי ליה. אע"ג דלעיל אמר גזוזא מידע ידיע בהוצא לא ידיע:

**Tanslation by Rabbi Ephraim Piekarski:**
**גייז¹ ליה חבריה ושדי ליה—His friend will cut it off and discard it**

OVERVIEW
The גמרא was discussing how to place the חזית when building a הוצא wall. If he arranges that the tips of the הוצא should extend into his neighbor’s חצר, his neighbor may simply cut them off. תוספות will explain this concern.
-------------------------
תוספות responds to an anticipated difficulty:
**אף על גב דלעיל אמר גזוזא מידע ידיע בהוצא לא ידיע:**
**Even though** the גמרא **previously stated** that **it is recognizable** when the חזית **is cut off.** There should, therefore, be no concern that the partner will dispose of the sign that he made for the הוצא wall. תוספותresponds; **by** הוצא **it will not be noticeable** if he cuts off the protruding הוצא. It is only by a חזית made of stone and mortar, that it is noticeable when it is removed. By a wall of הוצא where the חזית is made by protruding palm fronds, it is not noticeable.

SUMMARY
When a חזית of stone and mortar is removed it is readily apparent. However removing the חזית of a הוצא wall can remain unnoticeable.

THINKING IT OVER
How can we explain the הוה אמינא and מסקנא of this תוספות?

footnotes:
¹ This תוספות is referring to the גמרא on ב,ד.


###### Tosafot on Bava Batra 4b:6:1
[Tosafot on Bava Batra 4b:6:1](https://torahapp.org/share/book/Tosafot%20on%20Bava%20Batra/r/4b:6:1)

לאפוקי מדאביי. ואביי סבר דשפיר אית ליה למיתני תקנתא לרמאי:

**Tanslation by Rabbi Ephraim Piekarski:**
**לאפוקי מדאביי—To exclude from** what**אביי** said 

OVERVIEW
The משנה stated that if both partners in the בקעה field agreed to build the wall together; they should make a חזית on both sides, indicating the dual ownership. The גמרא questions the need for the double חזית. It would seem that no חזית would function as well. The גמרא replies that the משנה is giving this advice in a case where one of the partners (wrongfully) built a חזית which identifies him as the sole owner. To which the גמרא challenges, does the משנה concern itself with swindlers!¹ The conclusion of the גמרא is that the משנה is teaching us that (even) if the walls were made of הוצא, nevertheless a חזית is a sufficient marker to identify them both as owners. The משנה intends to discredit the idea of אביי that by הוצא, nothing less than a שטר can identify the owner(s). The question arises, how אביי will deal with this משנה. Why did the משנה teach us the דין of חזית in a case where שניהם רוצים?!
---------------------------
**ואביי סבר דשפיר אית ליה למיתני תקנתא לרמאי:**
**And** אביי **maintains that it is proper that the** משנה **offer a solution for a swindler.** In a situation where one of the partners (illegally) built a stone חזית on the wall, the משנה tells us that the other partner should make an additional חזית on the other side of the wall to indicate that it belongs to both of them. אביי will disagree with the premise of the גמרא that a משנה should not be concerned (solely) about swindlers.²

SUMMARY
According to אביי the reason that the משנה teaches us the last דין that they should both make a (stone) חזית is to protect people from swindlers.

THINKING IT OVER
What would be the דין according to אביי; in a case where the wall between two fields was made of הוצא, and the חזית indicated that there was one sole owner. The other partner however claimed that it belongs to both of them. Who would own the מקום and the fence?³

footnotes:
¹ משניות definitely teach us laws about swindlers, etc. However it is not within the purview of the משניות to teach us how to protect oneself from a swindler. The משנה need not teach us to lock away our treasures.
² Perhaps אביי generally agrees that the משנה does not offer a תקנתא לרמאי. Here however, once the רמאי built his חזית (perhaps even inadvertently), the משנה teaches us that the simplest way to rectify the situation is by building an additional חזית (not by destroying the original חזית and repairing the wall, etc.). וצע"ג.
³ See מהר"ם and נח"מ.


###### Tosafot on Bava Batra 4b:7:1
[Tosafot on Bava Batra 4b:7:1](https://torahapp.org/share/book/Tosafot%20on%20Bava%20Batra/r/4b:7:1)

אם עמד וגדר את הרביעית. ל"ג אם עמד ניקף דהא לכולהו לישני דגמרא קאי אמקיף בר מלישנא בתרא דקאמר מקיף וניקף איכא בינייהו והא דדייק בפרק כיצד הרגל (ב"ק דף כ: ושם) טעמא דניקף הא מקיף פטור היינו לההוא לישנא:

**Tanslation by Rabbi Ephraim Piekarski:**
**אם¹ עמד וגדר את הרביעית—If he arose and fenced in the fourth** side

OVERVIEW
The משנה is vague concerning the statement of ר' יוסי that 'אם עמד ניקף וכו. It does not state who was גודר; whether it was the מקיף or the ניקף that built the fourth wall. In other גמרות the text read explicitly 'אם עמד ניקף וכו. Our תוספות rejects this גירסא.²
--------------------------
**לא גרסינן³ אם עמד ניקף דהא לכולהו לישני דגמרא קאי אמקיף⁴ –**
**The text does not read; ‘if the encircled one arose’. For** in fact **according to** (almost) **all the interpretations** of the משנה **that the גמרא** states, the word 'עמד' **refers to the encircling** party; not (only) to the encircled party –
**בר מלישנא בתרא דקאמר מקיף וניקף איכא בינייהו⁵ –**
**Except for the last interpretation** in the גמרא, which **states; the difference between** the ת"ק and ר' יוסף will be whether **the מקיף or the ניקף,** built the fourth wall. According to this last opinion, the word עמד refers to the ניקף only and not to the מקיף. ר' יוסי maintains that only if the ניקף made the fourth wall then מגלגלין עליו את הכל. However the חכמים maintain that מגלגלין עליו את הכל regardless of who made the fourth wall.
תוספות anticipates a question on this statement that the term 'עמד' refers to the מקיף:
**והא דדייק בפרק כיצד הרגל (בבא קמא דף כ,ב ושם) טעמא דניקף הא מקיף פטור –**
**And** concerning **that which** the גמרא **infers in הרגל כיצד** **פרק,** in the discussion of whether זה נהנה וזה לא חסר is חייב or פטור. The גמרא infers from the statement of ר' יוסי that זה נהנה וזה לא חסר is פטור, for the גמרא there understands the word 'עמד' to refer to the ניקף, not the מקיף. As the גמרא there states that according to ר' יוסי **the reason** we are מגלגלין עליו את הכל is because **the** ניקף built the fourth wall (he showed that he is willing to spend money); therefore he has to pay for the rest, **however if the מקיף** built the fourth wall (also), the ניקף would be **פטור,** even though he is a נהנה. This proves that זה נהנה וזה לא חסר is פטור. This concludes the quote from that גמרא. Obviously that גמרא contradicts תוספות opinion that 'עמד' refers to the מקיף.
תוספות answers that there is no contradiction. The הגמרא סוגית that brought proof from our משנה –
**היינו לההוא לישנא:**
**It was according to that** last **לשון** in our גמרא, which interprets 'עמד' to refer to the ניקף.⁶ According to the other לשונות, however there would (seemingly) be no proof from our גמרא.⁷

SUMMARY
The גירסא in the משנה is ''ואם עמד וגדר וכו', not ''ואם עמד ניקף וגדר כו'. In fact according to almost all the opinions in the גמרא the rule of the משנה applies even if the מקיף was גודר. The גמרא in ק"ב that attempts to derive from our משנה that זה נהנה וזה לא חסר is פטור, indeed maintains that ואם עמד refers to the ניקף, and is following the לישנא אחרינא in our גמרא.

THINKING IT OVER
Can there be a סברא that if the ניקף made the fourth wall there will be less reason to be מחייב him than if the מקיף made the fourth wall?

footnotes:
¹ It would be beneficial to first learn the entire גמרא until the end of ב,ד, before studying this תוספות.
² It should be obvious that if גדר refers to the מקיף (and the ניקף is חייב) then certainly if the ניקף made the fourth wall he is חייב. The question is whether it means only the ניקף or perhaps the מקיף as well.
³ The משנה was vague as to who actually fenced in the fourth side.
⁴ Even if the מקיף made the fourth wall, the ניקף is responsible to contribute.
⁵ תוספות is referring to the לישנא אחרינא מקיף וניקף איכא בינייהו at the end of this עמוד.
⁶ Perhaps the גמרא there assumed that the expression 'ואם עמד וגדר', indicates that this is being done by a new person; one who is first now 'עמד וגדר', i.e. the ניקף. See תוספות ד"ה ור' יוסי on this עמוד.
⁷ We cannot infer anything from the fact that if the מקיף made the fourth wall the ניקף is חייב; because as the גמרא explains in ב"ק the מקיף is a חסר for he can claim את גרמת לי הקיפא יתירא. The proof can only be if the ניקף is פטור.


###### Tosafot on Bava Batra 4b:9:1
[Tosafot on Bava Batra 4b:9:1](https://torahapp.org/share/book/Tosafot%20on%20Bava%20Batra/r/4b:9:1)

דמי קנים בזול. וא"ת מאי שנא משדה שאינה עשויה ליטע דאם נטעה חבירו שלא ברשות אמר רב ושמואל בהשואל (ב"מ דף קא.) שמין לו וידו על התחתונה ואור"י דשאני הכא דמצי א"ל לדידי סגי לי בנטירא בר זוזא ומ"מ דמי קנים בזול יהיב ליה דאנן סהדי דאם היה מוצאם כ"כ בזול היה גודר בהם:

**Tanslation by Rabbi Ephraim Piekarski:**
**דמי קנים בזול—The discounted price of reeds**

OVERVIEW
חייא בר רב is of the opinion that ר' יוסי who maintains that the ניקף must pay for all four walls, is referring to a payment of דמי קנים בזול, not more. This is certainly much less than the actual cost of the walls (which are presumably made of stone) and it is also (presumably) less than the improvement made to the property of the ניקף. The value of his property increased more than the price of דמי קנים בזול. Our תוספות will explain why the owner pays only דמי קנים בזול.
--------------------------
תוספות asks:
**ואם תאמר מאי שנא משדה שאינה עשויה ליטע¹ דאם נטעה חבירו שלא ברשות –**
**You may ask; why is this** case **different from a field that is not intended for planting** trees**; that if his friend planted it without permission** from the owner **–**
**אמר רב ושמואל בהשואל (בבא מציעא דף קא,א.) שמין לו וידו על התחתונה –**
**רב and שמואל rule in** פרק **השואל** that **we assess for the** planter the value of the improvement in the field as opposed to his expenses for improving the field **and his hand is on the bottom (**he is in a weakened position)**;** i.e. The planter receives payment from the owner for the lesser of the two (if the expenses are less than the improvement, he only receives the expenses, and vice versa). The owner must pay regardless, since he derived benefit from someone’s expense. We see that in this case of planting, the owner must pay at least for the lesser of the two; either for the expenses or the improvement. The same should apply in the case of our משנה with the fencing. Why is it that the owner has to pay only דמי קנים בזול, which is less that either the improvement or the expenses?
תוספות answers:
**ואומר רבינו יצחק דשאני הכא דמצי אמר ליה לדידי סגי לי בנטירא בר זוזא –**
**And the ר"י says that here** in our משנה **it is different** from the case of the planter, **for** the ניקף **can claim; for me it is sufficient** to have it **watched for a** זוז**.** The value of the improvement is only a זוז. I could hire someone to guard my field for a זוז. Therefore for the owner the improvement is only worth a זוז.
תוספות anticipates the following question. If the owner claims that the improvement is worth only a זוז, why should he pay even for דמי קנים בזול? The owner should just pay a זוז.² תוספות replies:
**ומכל מקום דמי קנים בזול יהיב ליה דאנן סהדי דאם היה מוצאם כל כך בזול היה גודר בהם:**
**Nonetheless,** even though the owner claims that it is only worth a זוז, **he** still must **pay** the מקיף the price of **קנים בזול** **דמ**י, **for we** (the בית דין) **will testify that if he could find** the קנים **for this discounted price he would fence** in his property **with them.** A person will do something beneficial even if it is not that essential, if he can accomplish it for a substantially reduced price. He would rather his property be fenced in by using דמי קנים בזול than paying for a נטירא בר זוזא (which is cheaper). Therefore he must pay for the דמי קנים בזול, since he appreciates it and it is worth the price. His field did improve by (at least) דמי קנים בזול.

SUMMARY
In our משנה we do not rule that the ניקף should pay the lesser of either the expense or the improvement, because the ניקף can claim, this improvement is only worth the זוז that I (usually) pay the watchman. However he is obligated to pay דמי קנים בזול (not just a זוז), because there is the אנן סהדי, that were he able to obtain קנים בזול, he would certainly fence in his field with these קנים.

THINKING IT OVER
תוספות answers that the owner can claim that I require only a נטירא בר זוזא. Why did not תוספות answer that the owner can claim that I only require a גדר קנים (בזול),³ not a גדר אבנים?

footnotes:
¹ תוספות compares our משנה to a שדה שאינה עשויה ליטע, because in our משנה it is also שאינה עשויה to fence in fields in a בקעה.
² See ‘Thinking it over’.
³ This way תוספות would avoid his last question of 'ומ"מ דמי וכו'. See footnote # 2.


###### Tosafot on Bava Batra 4b:14:1
[Tosafot on Bava Batra 4b:14:1](https://torahapp.org/share/book/Tosafot%20on%20Bava%20Batra/r/4b:14:1)

שניה ושלישית לא. אומר ר"י דהיינו טעמא דאין לך אדם שלא היה מסייע לרביעית ע"מ שיהא גדור מד' רוחותיו ובקונטרס פירש לפי שכבר יצא מן השלשה מב"ד זכאי: הג"ה וקצת קשה דא"כ גם ברביעית יצא זכאי עד טפח אחרון ע"כ:

**Tanslation by Rabbi Ephraim Piekarski:**
**שניה ושלישית לא—**For the **second and third** wall he does **not** pay 

OVERVIEW
The גמרא explains the difference between the ת"ק and רבי יוסי (in one answer) that the ת"ק agrees that the ניקף must pay (jointly), but only for the fourth wall. The ניקף need not pay for the first three walls. ר"י maintains that he must pay (jointly) for all four walls. The question is according to the ת"ק, if the ניקף has to pay because he is deriving a benefit from the walls encircling his field, why is he exempt from paying for the first three walls. All four walls are contributing to the protection of his property. תוספות will discuss this issue.
---------------------------
**אומר רבינו יצחק דהיינו טעמא –**
**The** ר"י **says; that this is the reason** why he pays (jointly) [only] for the fourth wall [and not for the prior three walls] –
**דאין לך אדם שלא היה מסייע לרביעית על מנת שיהא גדור מד' רוחותיו –**
**Because you cannot** find **a person that would not** be willing **to assist in** paying **for a fourth** wall **for the purpose of being fenced in from all four sides.** Any person would be glad of this opportunity to pay (jointly) for only one wall and receive the protection of four walls. Therefore it is certain (even in the mind of the ניקף) that his field was improved at least for the (joint) cost of one wall.¹ He must pay for the improvement to his field.
**ובקונטרס פירש לפי שכבר יצא מן השלשה מבית דין זכאי:
However רש"י explained** that the reason the ניקף does not pay for the first three walls is **because he was already acquitted by בי"ד** from paying **for the three** original walls.² When the מקיף built the first three walls, then בי"ד did not hold the ניקף responsible at all, since three walls alone did nothing for the ניקף. That case is over with. The מקיף can only initiate a new דין תורה, on the fourth wall only.
There is a question on פירוש רש"י.
**הג"ה וקצת קשה דאם כן גם ברביעית יצא זכאי עד טפח אחרון –
A gloss: And there is a slight difficulty** with s'י"רש explanation **for if this is so;** the reason for non-payment on the three walls is on account that בי"ד acquits him since these walls provide no protection for the ניקף, then **also** concerning **the fourth** wall **he left** the בי"ד **acquitted until** the מקיף built **the last טפח.** Up to that point the ניקף is not properly protected; there is no reason that he should be responsible. The ניקף should only be responsible to assist in payment for the last טפח built in the fourth wall, when he receives adequate protection. The גמרא however says that the ניקף pays (jointly) for the entire fourth wall this would seem to contradict פירוש רש"י.**
עד כאן:**
**Until here** is the הג"ה. The הג"ה concludes here.

SUMMARY
תוספות and רש"י differ as to why the חכמים maintain that the ניקף is required to pay only for the fourth wall and not for the preceding three walls.
תוספות maintains that the ניקף cannot claim in regard to the fourth wall, when he is completely protected, that it is only worth for him a נטירא בר זוזא. It is obvious that anyone would be willing to assist in paying for (only) a fourth wall and receive in return a completed fence on all four sides. רש"י maintains that he does not pay for the first three walls since he was already (symbolically) acquitted by בי"ד from having to pay for them; since at that time they were useless, for he was not protected on the fourth side.
The הג"ה asks, that according to רש"י he should only be liable for the last טפח on the fourth side. Up until the completion of the fourth wall he was not properly protected and בי"ד will acquit him from being responsible.

THINKING IT OVER
1. תוספות mentions only the reason why he is חייב for the fourth wall; not why he is exempt from the first three walls. רש"י (quoted in this תוספות) explains only why he is פטור on the first three walls; not why he is חייב for the fourth wall. Can we combine the two פשטים?³
2. Can we infer from תוספות, whether, according to the ת"ק, the ניקף has to pay for a גדר אבנים or דמי קנים (בזול), or any other type of payment for this fourth wall.

footnotes:
¹ The ניקף cannot claim that for me a נטירה בר זוזא is sufficient. See previous תוספות ד"ה דמי. However concerning payment for the first three walls the ניקף can claim that for me נטירה בר זוזא is sufficient. I would never have paid so much money to have my property fenced in.
² תוספות (referring at least to the ה"הג in תוספות) does not understand רש"י to mean that the מקיף actually took the ניקף to a דין תורה and the ניקף was acquitted (for then the ה"הג would have no question). Rather it is to be understood that had the מקיף taken the ניקף to a ד"ת, the ניקף would have been acquitted.
³ See מהרש"א and בל"י אות צז.


###### Tosafot on Bava Batra 4b:17:1
[Tosafot on Bava Batra 4b:17:1](https://torahapp.org/share/book/Tosafot%20on%20Bava%20Batra/r/4b:17:1)

ורבי יוסי סבר אם עמד ניקף וגדר את הרביעית. אע"ג דעד השתא היה מחמיר כדמשמע לישנא דמגלגלין עליו את הכל להך לישנא לא הוי הכי דלשון אם עמד משמע ניקף:

**Tanslation by Rabbi Ephraim Piekarski:**
**ורבי יוסי סבר אם עמד ניקף וגדר את הרביעית—And ר"י maintains; If the encircled** party **arose and fenced in the fourth** wall, etc.

OVERVIEW
The גמרא offered various interpretations as to the מחלוקת between the ת"ק and ר"י in the משנה. According to all these interpretations – except for the last – ר"י deals more severely with the ניקף than the ת"ק does. תוספות will explain that both these positions can be derived from the wording of the משנה.
--------------------------
תוספות anticipates a difficulty:
**אף על גב דעד השתא היה מחמיר¹ כדמשמע לישנא דמגלגלין עליו את הכל² –**
**Even though up until now** the גמרא assumes that **מחמיר** ר"י **היה** **– was more stringent** than the ת"ק, as **the expression ‘we cumulatively** cast **upon him everything’**, **implies** that we deal severely with the ניקף. Why did this last לשון disregard this implication and insist that ר"י is more lenient with the ניקף?
תוספות responds:
**להך לישנא לא הוי הכי דלשון אם עמד משמע ניקף:**
**According to this לשון** **it is not so** that ר"י is more מחמיר than the ת"ק, despite the above mentioned implication, the reason is that **the expression ‘if he arose’** **indicates** that we are discussing (only) **the ניקף**. Therefore we are forced to conclude that if the מקיף built the fourth wall the ניקף is פטור. According to this לשון, the implication of the words 'אם עמד' is more compelling than the implication from the words 'מגלגלין עליו את הכל'.

SUMMARY
The expression מגלגלין עליו את הכל'' indicates that ר"י is more מחמיר than the ת"ק (hence all the לשונות in the גמרא [bar the last one]). The expression 'אם 'עמד seems to limit the liability to the ניקף only if he himself built the fourth wall (hence the לישנא אחרינא).

THINKING IT OVER
How will each of the opposing לשונות address the contradicting implications in the משנה?

footnotes:
¹ In all the interpretations ר"י dealt more severely against the ניקף compared to the ת"ק. This view is seemingly implicit in the language of the משנה.
² The expression 'מגלגלין עליו את הכל' implies that not only is he required to pay (something), but rather he must pay for everything.


###### Tosafot on Bava Batra 4b:17:2
[Tosafot on Bava Batra 4b:17:2](https://torahapp.org/share/book/Tosafot%20on%20Bava%20Batra/r/4b:17:2)

הגה"ה כתב בספרים אבל מקיף לא יהיב ליה אלא דמי רביעית. וקשה דמנלן דיהיב ליה אפי' דמי רביעית דילמא לא יהיב ליה כלל וכן משמע בפ' כיצד הרגל (בבא קמא כ: ושם ד"ה טעמא) דקאמר טעמא דניקף הא מקיף פטור ש"מ זה נהנה וזה לא חסר פטור ודחי שאני התם דא"ל לדידי סגי לי בנטירא בר זוזא מיהו יש לדחות דה"ק לדידי סגי לי בנטירא בר זוזא הלכך פטור מלסייע לד' רוחות אבל רביעית יסייע דאין לך אדם שלא יסייע לרביעית שיהיה גדור מארבע רוחותיו:

**Tanslation by Rabbi Ephraim Piekarski:**
**הגה"ה¹ כתב בספרים² אבל מקיף לא יהיב ליה אלא דמי רביעית—A gloss: It is written in** certain **text, ‘however if the מקיף** made the fourth wall, the ניקף **pays him only the value of the fourth** wall’.

OVERVIEW
The לישנא אחרינא interprets s’ר' יוסי position, that only when the ניקף made the fourth wall is he liable to assist in payments for all four walls, but not if the מקיף made the fourth wall. In our texts, the conclusion is that if the מקיף made all four walls the ניקף pays nothing at all. תוספות cites other texts where it states that if the מקיף made the fourth wall then (according to ר"י) the ניקף must assist in paying for the fourth wall (only). תוספות will explain the rationale for this ruling, as well as why it does not contradict a גמרא in ב"ק.
-----------------------
תוספות asks:
**וקשה דמנלן דיהיב ליה אפילו דמי רביעית דילמא לא יהיב ליה כלל –**
**And this is difficult; for how do we know that** the ניקף is required **to pay even for the fourth wall?! Perhaps the** ניקף **need not pay anything** if the מקיף made the fourth wall. We are now assuming that the term 'ואם עמד' refers to the ניקף; that only then is he חייב since דגלי דעתיה דניחא ליה; implying that if the מקיף made the fourth wall and there is no גילוי דעת, the ניקף is not responsible for anything.
תוספות cites a גמרא which supports his contention:
**וכן משמע בפרק כיצד הרגל (בבא קמא דף כ,ב ושם דיבור המתחיל טעמא) דקאמר –**
**And this is also seemingly indicated in פרק כיצד הרגל,** that if the מקיף made the fourth wall the ניקף is completely פטור, **for** the גמרא **says** there –
**טעמא³ דניקף הא מקיף פטור שמע מינה זה נהנה וזה לא חסר⁴ פטור –**
‘**The reason** ר"י maintains that מגלגלין עליו את הכל is because **the** ניקף **fenced in** the fourth wall⁵ **however had the מקיף** fenced in the fourth wall, the ניקף would have been **פטור**; **we can derive from this** ruling of ר"י that in the case where **one derives a benefit and the other** (the benefactor) **is not lacking** on account of this derived benefit, the beneficiary **is exempt’** from paying to the benefactor; since he is not causing the benefactor any monetary loss.⁶ This is a case of זה נהנה וזה לא חסר and he is פטור.⁷ The גמרא there continues –
**ודחי שאני התם דאמר ליה לדידי סגי לי בנטירא בר זוזא –**
**And** the גמרא there **rejects** this proof. It is possible to assume that זה נהנה וזה לא חסר is indeed חייב, the reason that the ניקף is פטור is **because** the ניקף **says to** the מקיף ‘**a** זוז **worth of watching is sufficient for me’.** My derived pleasure from your wall is worth only a זוז to pay for a watchman. A wall is not necessary; it is extravagant. Therefore the נהנה is only a זוז (which he will be obligated to pay him), but not for the wall(s). However by a regular נהנה, perhaps he would be required to pay for the entire הנאה. This concludes the גמרא that תוספות is citing from ב"ק. It seems from that גמרא that the ניקף is obligated to pay a זוז (at most), but not for the fourth wall, as indicated by the גירסא that תוספות quoted. How can we reconcile this גירסא (which requires the ניקף to pay for the fourth wall), with the גמרא in ב"ק (which seems to be saying that the ניקף is liable only for a נטירא בר זוזא)?!
The original question of תוספות is based on logic. What reason is there to say that according to ר"י the ניקף must pay for the fourth wall? The second question was that this גירסא seemingly contradicts a גמרא.
תוספות replies:
**מיהו יש לדחות דהכי קאמר לדידי סגי לי בנטירא בר זוזא הלכך פטור מלסייע לד' רוחות –**
**However, perhaps** this proof **can be rejected.** There is no proof from ב"ק that the ניקף pays only for a נטירא בר זוזא, **for this is what** the גמרא in ב"ק **is saying.** The ניקף is arguing that **for me a זוז worth of security is sufficient**. I do not require a more expensive protection,⁸ **therefore** the ניקף **is exempt from** any requirement to **assist** in the building of the **four walls**; since he has no הנאה which is worth that much money –
**אבל רביעית יסייע דאין לך אדם שלא יסייע לרביעית שיהיה גדור מארבע⁹ רוחותיו:**
**However,** for **the fourth** wall, he is obligated **to assist** in paying for its cost **for there is no person who would not** be willing to **assist in the fourth** wall if he knows **that he will be fenced in from all four sides.** No one will turn down such a bargain. It is worth for him to lay out a minor expense to derive a significant improvement in his property. It is considered that his הנאה is worth the contribution for the fourth wall.¹⁰

SUMMARY
In the לישנא בתרא there are two different גירסאות that dispute what position does ר' יוסי maintain, in the case where the מקיף made the fourth wall.
Some texts maintain that ר"י is of the opinion that the ניקף owes nothing if the מקיף built all four walls. This position is seemingly supported by the גמרא in ב"ק which articulates the argument of the ניקף; ‘I only require a נטירא בר זוזא’. This seemingly exempts him from any (additional) payments.
The texts that maintain the even according to ר"י the ניקף must pay for the fourth wall, will argue that even though a נטירא בר זוזא is sufficient, nevertheless the ניקף must pay for the fourth wall. This is based on the assumption that any person is willing to assist in the building of one wall when in return, he is fenced in on all sides.

THINKING IT OVER
1. Why did not תוספות ask this same question on the previous לשונות who interpreted the position of the ת"ק that the ניקף must pay only for the fourth wall, if the מקיף built all four walls?¹¹
2. תוספות cites the גמרא in ב"ק as proof that ר"י maintains that the ניקף owes nothing if the מקיף made all four walls. To prove his point תוספות quotes the 'ודחי' of the גמרא as well. Seemingly תוספות could have proven his point from the original ראיה. It states there 'הא מקיף פטור'. That would seemingly prove that he is פטור completely. Why was it necessary for תוספות to cite the concluding 'דיחוי' of 'שאני התם וכו, as well?¹²
3. תוספות first question is why we should assume that he is required to pay for the fourth wall. Seemingly תוספות has already answered this question in תוספות ד"ה שניה on דף ד,ב in the same manner as he explains it here. Why does he repeat the same answer twice?

footnotes:
¹ Seemingly this תוספות was not part of the original תוספות but was included as an addendum from (presumably) other בעלי תוספות. See תוספות ד"ה הג"ה on דף ג,ב.
² This תוספות is discussing the גמרא at the very end of דף ד,ב.
³ The הגהות הב"ח amends this to read 'טעמא דגדר ניקף'.
⁴ The גמרא there was discussing a case of זנוזל"ח, wherein a tenant lived in a vacant property of a neighbor. The tenant was נהנה; however the owner of the property was לא חסר, for he had no intention of renting out this property.
⁵ See תוספות on דף ד,ב ד"ה אם.
⁶ The מקיף made the fourth wall for his own benefit, that his fields should be protected. The s'ניקף field is then automatically protected. The ניקף is deriving a benefit from the מקיף. However the benefit that he is deriving is not causing any loss to the מקיף. The מקיף is making the walls for himself.
⁷ See ‘Thinking it over # 2.
⁸ See תוספות on דף ד,ב ד"ה שניה and ד"ה דמי קנים.
⁹ תוספות not only resolves the contradiction from ב"ק, but in addition, maintains that logic dictates that the ניקף be responsible for the fourth wall.
¹⁰ It would seem that the value of the הנאה is commensurate with the amount of money one would be willing to spend in order to receive this הנאה. The ניקף is willing to spend money, assisting for the fourth wall, in order to be fenced in completely. Therefore he is נהנה the cost of a wall, not merely a נטירא בר זוזא.
¹¹ See (עד"ז in the) רש"ש.
¹² See footnote # 7.