פירוש על בבא מציעא 9:1

But according to [Rav Sheshet], the one who says that [where the debtor says]: Here you are, [he is] exempt; why was [it] necessary [for the] verse [to exclude]. The Gemara earlier on 4a assumed that whenever a defendant admits that he owes the plaintiff land, it is by definition a case of ‘הילך - Here, it is yours!’, since the land is available to be returned to the plaintiff. Based on this assumption, the Gemara now asks: If when a defendant says ‘הילך - Here, it is yours!’ he is exempt from swearing, why must the Torah teach us that land cannot generate an oath obligation, when a defendant admits owing land, he would be exempt from swearing because it is a case of ‘הילך - Here, it is yours!’?
It seems from the Gemara’s question that we have this difficulty understanding the need for an exclusion of land from an oath obligation only if we hold that when the defendant says, ‘Here, it is yours!, he is exempt. However, if we hold that in cases of ‘Here, it is yours!’, the defendant is obligated to swear, there is no difficulty. Tosfos will demonstrate that even if we hold that one is liable in cases of ‘Here, it is yours!, there would still be a difficulty with the need for an exclusion for land from an oath obligation.
Earlier on 3b we learned in Tosfos ד'ה בכוליה בעי דלודי ליה, that the reason one who admits partially to the plaintiff’s claim is obligated to swear and we do not exempt him from the oath because he would not have the audacity to deny his debt in the face of his creditor, is because we do not view his partial denial as audacity, rather, he is merely evading his creditor and stalling for time. We may summarize this as follows:
A) A counterclaim is not a demonstration of audacity if it can be explained as a means of ‘evading the creditor’. It also follows that the reverse is also true:
B) If a counterclaim cannot be dismissed as a means of ‘evading the creditor’, it is viewed as a demonstration of audacity and we rule that a person does not have the audacity to deny a creditor’s claim in his face. He must therefore be believed that he is telling the truth.
Tosfos earlier on 3b: Therefore, it can be said that the words “and he wants to admit to the entire claim” are in response to this underlying question: Since we have just said that one does not have the audacity to lie in the face of his opponent who knows the truth, then when he says he only owes fifty zuz, we should assume that it is true that he does not owe him more. Why must he swear to defend his claim? He should be believed with a migo that he could have denied the entire claim of the plaintiff? Tosfos is assuming at this point that even a partial denial is essentially audacious. We should therefore rule that since he does have the audacity to deny part of the claim, we should believe him because he has a migo that he could have denied the entire claim. We cannot say that he does not have the audacity to do so, because he is presently exhibiting audacity in his denial of half the claim.
[The Gemara] answers: That this partial denial is not a demonstration of his inherent ability to make an audacious counter-claim, because the partial admission is his way of ‘evading the creditor’ till he will have sufficient funds to pay. It is not at all a demonstration of audacity.
When a defendant denies that he owes the plaintiff land, the idea that he might be ‘evading the creditor’ to stall for time is inapplicable, because the land is always here and available. We should therefore rule that when one denied a claim against himself, we believe him because he would not have the audacity to deny his debt in the face of his creditor.
This is bewildering! For even according to the one who says: In a case of ‘Here, it is yours!’ the defendant is obligated to swear, why is a verse needed to exclude land from generating an oath obligation, for when dealing with land the possibility of ‘evading the creditor’ is inapplicable? The portion of the land that he is denying is always here and available and can be returned immediately.
The Gemara on 6a is discussing שבועת היסת - the ‘oath of incitement’ instituted by Rav Nachman. The Gemara is attempting to prove that even when ‘evading the creditor’ is inapplicable, there is an obligation to swear. Tosfos asks: But even in the case of one who denies the claim entirely, there is a possibility that he is attempting to evade the creditor? Tosfos concludes that Rav Nachman requires an oath even when ‘evading the creditor’ is totally inapplicable. For example: When the plaintiff claims that the item the defendant has in his hands is mine and the defendant denies it, Rav Nachman also requires an oath by the defendant. Certainly, there is no possibility of ‘evading the creditor’ when the disputed item is available in our presence.
Tosfos there ד'ה אלא הא argues that Rav Hai Gaon also holds that Rav Nachman’s oath is required even when ‘evading the creditor’ is not a factor. His example is that one is required to swear even when the issue is about land. We see that in regard to land ‘evading the creditor’ is inapplicable because the land is always here.
So too, Rav Hai Gaon explains that we do swear שבועת היסת - the ‘oath of incitement’ when the claim is about land, even though ‘evading the creditor’ is inapplicable.
So does [the Gemara]¹See מהרש"א who offers the following amendment of the text, which is what we followed in our explanation of Tosfos: וכן פריך לקמן וכי כופר. ask later according to Rav Hai as explained by Tosfos (See 6a תוס' ד'ה אלא): That the Gemara on 6a is referring to a ruling that one must swear according to Rav Nachman even when the dispute is about land. We therefore see from Rav Nachman that even when there is no possibility of ‘evading the creditor’ an oath of incitement is required by Rabbinic law. Based on this conclusion Tosfos now continues his question: When [a defendant] denies owing some of the land that the plaintiff is claiming, he should be exempt from paying and swearing, for we should believe him, since one does not have the audacity to lie in the face of his creditor. As explained, evading the creditor cannot be used as an explanation for his ability to lie in this instance, since the land he denies is always here.
Perhaps, even in regard to land ‘evading the creditor’ is somewhat applicable, for perhaps [the defendant] pledged [the land] to a third party as security for a debt and he cannot presently return it to its true owner. He thinks that he will deny the plaintiff’s claim until he will accumulate cash and will pay the debt to the third party and then return the land to the plaintiff.

Why is it necessary to have a [special] verse to exclude land [from an oath obligation]? As explained in the introduction to the previous Tosfos, the Gemara holds that if the rule in cases of ‘הילך - Here, it is yours!’ is that one is exempt from swearing, cases involving land should always be exempt from an oath obligation, because one’s admission that he owes land is tantamount to ‘הילך - Here, it is yours!’ since the land is always here and available. If so, why is a special verse needed to exclude cases of ‘הילך - Here, it is yours!’ from an oath obligation?
The assumption of this Gemara’s question is that there is in fact a superfluous verse to exclude land from an oath obligation. Tosfos re-examines this assumption! This is bewildering! But there is no superfluous verse to exclude land from an oath obligation? Rather, it is excluded from a generalization, specific and generalization. Perhaps the Gemara’s question is that this system is not needed? Tosfos explains that this is not so. The generalization, specific and generalization, is needed to exclude documents from an oath obligation. The same generalization etc. can be used to exclude land if needed, but it is certainly not superfluous?
Tosfos is convinced of the strength of his challenge and must resort to a different explanation of the Gemara’s question. We can answer: That the Gemara’s question is not about a superfluous verse, rather, [the Gemara’s] question is why did the Tanna need to derive that land is exempt from an oath from the generalization and specific etc. system, since disputes involving land are inherently cases of ‘הילך - Here, it is yours!’, which are automatically exempt from an oath obligation.
A short review of the Gemara on 3a about the exemption of ‘הילך - Here, it is yours!’: Rav Sheishes says: A defendant who says: ‘הילך - Here, it is yours!’ is exempt from an oath obligation. What is the reason?
Since the defendant says: ‘הילך - Here, it is yours!’, the money that he admitted owing, are as if the lender is holding them. In regard to the other fifty, the borrower denies owing them entirely. Therefore, this is not a case of one who admits part of the claim against him.
It is obvious that the rationale for exempting one from an oath in a situation of ‘הילך - Here, it is yours!’, is not one that is applicable to all oath obligations. Its logic is exclusively relevant to the oath of one who partially admits the claim against him.
If you ask: Let us say that [the Tanna] who discusses an exemption for land needed to exclude land from the oath generated by a single witness? Why is the Gemara convinced that he spoke of this exclusion for the oath of one who partially admits the claim against him?
However, we can answer: Because the Mishna’s discussion of not swearing about land is speaking about the oath of one who partially admits the claim against him. It is therefore reasonable to assume that the exclusion he discusses is for this oath. Thus proving that even in case of ‘הילך - Here, it is yours!’ one is obligated to take an oath.