Commentary for Shevuot 7:2
הַנִּגְזָל כֵּיצַד, הָיוּ מְעִידִין אוֹתוֹ שֶׁנִּכְנַס לְבֵיתוֹ לְמַשְׁכְּנוֹ שֶׁלֹּא בִרְשׁוּת, הוּא אוֹמֵר כֵּלַי נָטַלְתָּ, וְהוּא אוֹמֵר לֹא נָטַלְתִּי, הֲרֵי זֶה נִשְׁבָּע וְנוֹטֵל. רַבִּי יְהוּדָה אוֹמֵר, עַד שֶׁתְּהֵא שָׁם מִקְצָת הוֹדָאָה. כֵּיצַד, אָמַר לוֹ שְׁנֵי כֵלִים נָטַלְתָּ, וְהוּא אוֹמֵר לֹא נָטַלְתִּי אֶלָּא אֶחָד:
One who has been robbed — how so? If they testified against him that he entered the other's house to take a pledge from him without being authorized to do so, [as when witnesses saw him enter the other's house with nothing in his hand and he left with vessels projecting from the folds of his garment] — He says: "You took my vessels"; the other says: "I did not," he (the claimant) swears and takes. [For the indications are (that he did steal). For the witnesses testify that he took a pledge without authorization. This, when he claims something which he is likely to own, but if he claims "a silver chalice," or the like, which he is not likely to own, it is not for him to swear and take (in all instances), but the claimee swears and exempts himself.] R. Yehudah says: (He does not swear) unless there is partial admission. How so? As when he said: "You took two vessels," and the other said: "I took only one."
Bartenura on Mishnah Shevuot
English Explanation of Mishnah Shevuot
If they testified of a man that he entered into another’s house to take a pledge without permission, and the other says, “You have taken my vessels, and he says, “I have not taken them,” he takes an oath, and takes back his vessels.
Rabbi Judah says: “[There is no oath] unless there is partial admission: How so? He said to him, “You have taken two vessels,” and the other says, “I have taken only one.”
This mishnah discusses the oath taken by one who has been robbed. Through this oath the one who was robbed can recover his money from the robber.
The second type of person who is allowed to swear and collect is one who has been robbed. In the scenario presented in the mishnah Reuven enters Shimon’s home to take Shimon’s property as a pledge against Shimon’s debt to Reuven, but Reuven did not have permission, neither from Shimon nor from the court, to do so. Shimon claims that Reuven took his vessels when intruding into the house. If Reuven denies having done so, Shimon may swear and take from Reuven the value of the vessels that he has claimed. The reason that Shimon is allowed to swear and thereby collect is that Reuven is punished for having illegally entered Shimon’s house. Since he already broke the law, we do not trust him to deny having further broken the law.
According to Rabbi Judah, he is allowed to swear and collect only if Reuven denies part of the claim and admits to the other part. If Reuven denies the entire claim, Shimon cannot swear and thereby collect.