Our Gemara on Amud aleph uncharacteristically asks why the Torah obligates an oath by a person who partially admits, but exempts the person who flat out denies the claim. Usually the Gemara asks the “what”, but not the “why.”  For example, a Gilgul Shevua, on the face of it, makes little sense. (An additional oath, levied on the defendant once he already is obligated in a first oath, even if a second claim on the part of the plaintiff is lacking evidence.) Why should a claim with little merit, that ordinarily would not incur an oath, now, all of the sudden obligate the defendant? The Gemara never asks why Gilgul Shevua, even though it seems even less logical than the oath of partial admission, and otherwise many details of the “what” for gilgul shevua are discussed later on Daf 4 (where I hope to offer a possible explanation for the unique legal process.)  

Our Gemara delves into the logic behind the oath of partial admission, because the underlying logic has halakhic implications and also allows us to resolve a logical problem. The entire idea of requiring the person who makes a partial admission to take an oath, on the surface, is apparently absurd.  If we don’t trust him, why would we think he wouldn’t lie under oath?   And if we find his claim believable, why require an oath? The answer has to do with a perception of human psychology and motivations. It is possible  that the person owes the full amount, didn’t have enough money to pay and was afraid that he would be stripped of his possessions. He’s not really a crook and intends to pay back the full amount once he is more solvent. Meanwhile, he will admit to a portion of the amount he owes and pay it down. Since he is not a full fledged criminal or habitually deceitful person, the obligation to swear causes him to reconsider his claim and fess up. He might have been tempted to tell a white lie, but he’s not going to swear falsely.

There is a famous question (Shu”t Mutzal Me-Eish 53:2) as to why is any plaintiff allowed to push a lying defendant to make an oath? From the perspective of the plaintiff, who knows the truth, he is definitely causing the defendant to sin (lifnei iver)? It is a prohibition to cause a person to sin (Chinuch 232), so perhaps one should forgo monetary claims, to avoid causing the liar to swear. We are obligated to give up all our money so as not to violate a prohibition (see Shulchan Aruch OC 656:1), so why not here do the same to avoid lifnei iver? 

To answer this, Radbaz (IV:223) holds that in certain situations where the sinner is brazen and trespassing, we do not protect him. The adage is, “Feed it (the poison) to the sinner and let him die”, Bava Kama 69a. A different and logical answer given by Kley Chemda (beginning of Mishpatim) is by dint of the fact that the Torah allows for an oath to help resolve a court matter, it is de facto permission to override the prohibition of lifnei iver. This is similar to the idea that even Hashem allows his name to be erased for the sake of promoting peace (Sotah 53b). 

Sefer Daf Al Daf says his own answer, that it is not truly lifnei iver, as maybe the person will chicken out and be afraid to lie, as we saw from our gemara’s discussion.  Even in situations where the Torah is not obligating an oath, such flat out denial, but the Rabbis still required an oath, we can use the reasoning supplied from our Gemara. That is to say, we can understand that there might be rationales for certain types of thievery and denial, while a person still would not go as far to make a false oath, which is a more grievous sin than mere theft. Also, from the story of Shlomo Hamelech and the baby discussed in yesterday’s daf, we see the idea that sometimes a ruse is useful to bring about justice, even though there is an aspect of insincerity. (See the blogpost Psychology of the Daf Bava Metzi’a 2.) The gemara’s formulation shows that the Torah can engage in morally justified psychological manipulations in order to flush out a liar.