Changing the requirements of a monetary case

Question

In Sanhedrin 23: Rashi: נמצאת כת שניה קרובים או seems to imply that if the בעל דין states that he has 2 sets (4 people) of kosher עדים that he now is required to bring forth 2 sets of kosher עדים. It's known that all you need is 1 set (2 people) of kosher עדים to win a monetery case in court but it seems that if you claim you have more then 1 set, you must now bring however many sets you said you had and if you fail to do so, you lose the case. Why do the requirements of the case (how many עדים need to be brought) change simply by the בעל דין making a statement like this?

Answer 1

POINT BY POINT SUMMARY Sanhedrin 23b

Explains that this is an argument discussing whether a litigant (Reuven) is able to join with a witness (David) in order to disqualify one of the pairs of witnesses that his opponent (Shimon) claims to have. If Shimon does have two pairs of witnesses, then even if one pair has been disqualified, the other pair is sufficient. See number 5 in the summary below.

Number 6 below says that once Shimon makes a claim, he must follow up that exact claim. However, that also means that Reuven cannot join with David to disqualify one of the two pairs.

(n) Answer #3 (Rav Dimi): The Tana'im argue when Shimon said that he has two pairs of witnesses:

1. Version #1 (our text, Tosfos): R. Meir says that Shimon must defend his claim (therefore, Reuven can join David to disqualify one pair of Shimon's witnesses - Reuven is not Noge'a, because in any case Shimon must bring other witnesses);

2. Chachamim say, Shimon need not defend his claim (therefore, Reuven is Noge'a, he cannot join to disqualify witnesses).

3. Version #2 (our text, Ramah): R. Meir says that Shimon must defend his claim (therefore, Reuven can reject one pair of Shimon's witnesses without proof, Shimon must bring another pair);

4. Chachamim say, Shimon need not defend his claim (therefore, Reuven cannot reject witnesses without proof).

5. Version #3 (Rashi): R. Meir says that Shimon need not defend his claim (therefore, Reuven can join to disqualify one pair of Shimon's witnesses, since it suffices for Shimon to bring the other pair of witnesses);

6. Chachamim say, Shimon must defend his claim (therefore, Reuven cannot join to disqualify witnesses, for this would destroy Shimon's claim, Reuven is Noge'a). (end of Version #3)

7. All agree that if Shimon never claimed to have two pairs of witnesses, Reuven cannot join to disqualify witnesses.

Answer 2

There is firstly a formulation problem.

I will re-write the question with my own words.

1. The main purpose of the Beth Din is to achieve justice.
2. So, if Reuven has only 2 good witnesses, it's enough for the Beth Din.
3. And we find out here an additional area of concern for Beth Din.
4. What is this concern?
5. This Concern is called "?צריך לברר?/אין צריך לברר".

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ANSWER
1. But advocacy element of Shim'on is a part of the alleged truth. He lets the Beth Din believe that he can equally use anyone of the two groups. The Beth Din would taken anything.
2. If he said that he will provide two groups of testimonies, he itself expressed the will to allows the other side to disqualify the first group.
3. Afterward, this allowance becomes one of the rules that he himself chosen. He do not lacked seriousness.
4. So if it turns that he did not provide the second group, this shows as if he declined to call the second group of witnesses.