Rashi: It refers to someone who is asked by a litigant to swear that, if he is able to testify on his behalf, he will do so ? and he did in fact, witness the transaction in question.

Targum Yonasan: It is referring to someone who hears a person making an oath of curse. ¹

Oznayim la'Torah: The Torah is referring to four different cases where Reuven knows testimony on behalf of Shimon but fails to testify: 1. Where he withholds it without being asked to testify; ² 2. Where he is the only witness and Shimon actually asks him to testify; ³ 3. Where there is a second witness and Shimon asks them to testify without an oath; ⁴ 4. Where Shimon asks them to testify under oath, and they deny any knowledge of the issue. ⁵

Ramban: Testimony that is to the advantage of the litigant who is making him swear. ¹

She'iltos de'R. Acha'i Ga'on": To teach us that, although he is only Chayav a Korban, if he swears, it is considered a sin to refrain from testifying even without a Shevu'ah. ¹

Tosefta Shevu'os, 1:2: To teach us that he is Chayav, irrespective of which language he made the Shevuah.

Tosefta Shevu'os, 1:3: To preclude a deaf person from the Chiyuv.

Shevu'os, 35b: "Alah" is synonymous with "Shevu'ah". ¹

Shevu'os, 35a: It implies that the litigant asks the winesses directly, but not if he says to a group of people containing him 'Mashbi'a Ani aleichem Im Atem Yod'in li Eidus, she'Tavo'u Vete'iduni!' It does however, include where he says ' 'Kol ha'Omdim Ka'an'. ¹

Yerushalmi Sanhedrin, 3: Bearing in mind that, whenever the Torah writes "Eid" S'tam, it means two witnesses, ² it precludes where the litigant says to one witness 'I accept you as if you were two witnesses!'

Shevu'os, 35a: It implies that the testimony must precede the Shevu'ah, and that consequently, if Reuven says to Shimon 'I am Mashbi'a you that, when you will know testimony on my behalf, you will come and testify', Shimon is Patur.

Ramban #1 (citing Shevu'os, 33b): It implies a. 'Seeing without knowing' - Where Reuven claims that he counted out to Shimon in front of witnesses, which Shimon denies; b. 'Knowing without seeing' - Where Reuven claims that Shimon admitted to him that he owed him money in front of witnesses which Shimon denies. ¹

Ramban #2: It implies that he is a witness - inasmuch as he either saw the entire transaction or that he knows about it (because the other litigant admitted it in his presence).

Targum Yonasan: It implies that either he himself is a witness, or he saw somebody transgressing an oath or he knows of somebody who transgressed an oath - and declines to inform the Beis-Din. ²

Tosefta Shevu'os, 3:6: They preclude someone who is blind in both eyes ¹ and a Shoteh ² respectively, from a Korban Shevu'ah.

Yerushalmi Shevu'os, 5:1: We learn from Shevu'as ha'Pikadon, in Pasuk 21, via a Gezeirah Shavah "Nefesh" "Nefesh" that he is Chayav.

Kesuvos, 18b: It implies that, once a witness has testified, he cannot testify again (change his testimony). ¹

Moshav Zekenim: In order to read "Lo" like with a 'Vav', as if to say - if he testified for him, he cannot retract and testify differently.

Shevu'os, 35a: To Darshen 'Im lo Lo Yagid' - he is only Chayav a Korban Shevu'ah if he swears to the litigant himself, but not if the litigant sends a Shali'ach and makes him swear.

Rashi (in Shabbos, 68b) and Ramban: Because in this particular case, he is subject to a Korban even be'Meizid. ¹

Yoma, 74a: To preclude from a Korban Shevu'ah someone who is unfit to testify ? such as a professsional gambler. ¹

Gitin, 71a: To preclude someone who is dumb.

Shevu'os, 35a: To preclude witnesses who only received their information from another witness ('Eid mi'Pi Eid') or where one of the witnesses is a relative or Pasul le'Eidus.

Yerushalmi Sanhedrin, 3:9: To extrapolate that only Kasher witnesses ¹ whose testimony would have caused the litigant to pay money are Chayav a Korban Shavu'ah.

Sanhedrin, 37b: To teach us that in spite of the harsh warning in connection with the results of testifying falsely ² they are not permitted to withdraw from the obligation to testify. ³

Shevu'os, 33a: To extrapolate that the witnesses are only Chayav a Korban Shevu'ah if the litiganr nade them swear in Beis-Din - where they would have rendered the litigant Chayav, but not if he made them swear outside Beis-Din.

Bava Kama, 56a: It means that the witnesses are only Chayav be'Dinei Shamayim for failing to testify but are not punishable be'Dinei Adam. ¹

Da'as Zekenim: To teach us that the punishment for Shevu'ah is great, and that Shogeg is considered like Meizid. ¹

Refer to 5:1:4:1.

Moshav Zekenim: In order to read "Lo" like with a 'Vav', as if to say - if he testified for him, he cannot return and testify again [differently].