The Gemara on today’s daf (=page) relates the following case:
A certain person grabbed a silver piece from his friend. He was brought before Rabbi Ami and Rabbi Abba was sitting before him. The claimant brought a single witness who testified that the defendant had taken the silver piece from him, a claim to which the defendant readily agreed saying: “Yes, I took it, but I was only taking back property that belonged to me!”
Hearing the exchange of claims, Rabbi Ami mused: “How should the judges rule on this case? On the one hand, we cannot make him pay, since there is only a single witness. On the other hand, we cannot trust him to take an oath that he took what belonged to him (the ordinary ruling in a case where there is a single witness) since he has admitted that he is a thief?” Rabbi Abba responded that we will make him pay for the silver, since he is someone who is obligated to take an oath, and anyone who is obligated to take an oath and cannot do so, must pay.
One question raised regarding Rabbi Ami’s musing is his assumption that the defendant cannot be trusted since he admitted his guilt in taking the silver. In fact, the defendant claims that his actions were totally within his rights, since he was just taking back his property, and there is only a single witness who accuses him of wrongdoing. Some manuscripts leave out the argument that the defendant is considered to be a thief, and instead simply have the Gemara read “he admits it.” The meaning of this statement becomes that he must pay since he cannot swear regarding this case. His inability to swear does not stem from the fact that he is a thief, rather it is because he cannot deny the testimony of the witness, since he has already admitted that what the witness said is true – he did take the silver.