Mishnah Shevuot 4-10

Here, the Mishnah is going to talk about somebody who puts an oath on a group of people without saying which specific witnesses he would like to put that swear on. The Mishnah says, “If there was a person who stood up in the synagogue and said to all those who were in front of him the following: ‘I’m putting a swear onto all of you: if any of you know testimony that would be helpful to me, you’ll come forward and testify on my behalf.’” There were witnesses in the crowd, and they knew something that would have been helpful to this person, but they denied knowing that testimony. They would not be obligated to bring a korban (sacrifice), because witnesses would not become obligated until the person trying to put a swear upon them specifically targeted and addressed them when he was putting the swear on them. In this case, he never specified a person or a pair of individuals that he wanted to talk to. He had no idea who was really in the crowd or who knew anything. So he spoke in very general terms to the whole synagogue, and therefore he never put a swear onto anybody in particular who may be; therefore, they would be exempt.