Ketubot, Chapter Thirteen, Mishnah Four
In chapter six of Shevuot we learned that one who admits to part of a debt, must take an oath that he does not owe the rest. Our mishnah deals with the case where Reuven claimed that Shimon owed him jars of oil and Shimon admitted only that he owes empty jars. The question is, is this a case of partial admission. The same mishnah was brought in Shevuot 6:3.
1) If he claims from his neighbor jars of oil, and he admits [his claim to the empty] jars,
a) Admon says, since he admits to him a portion of the claim, he must swear.
b) But the Sages say: the admission is not of the same kind as the claim.
2) Rabban Gamaliel said: I agree with the words of Admon.
In this scenario Reuven claimed that Shimon owed him jars of oil. Shimon admitted that he owed Reuven jars but denied that he owed the oil. According to Admon, an early Sage, this is considered a partial admission to the claim: Reuven claimed jars and oil and Shimon admitted only to the jars but denied the oil. Therefore Shimon must swear that he doesnt owe the oil. The other Sages who disagree with Admon say that Reuven really only claimed oil. The fact that Reuven said jars of oil was in order to express the amount of oil that he was claiming from Shimon. Since the claim and the admission were of different kinds, Shimon does not swear. Rabban Gamaliel says that he agrees with Admon.