Question

Hello Rabbi,
During my study of the book Sha’arei Yosher I came across a passage that I’m unable to understand, and since I know from the blog and the lectures and so on that this book is dear to you, I’m turning to you with a question. Rabbi Shimon discusses there, in the context of imperceptible damage, the case of one who says to his fellow, “The pure items that I handled with you became impure,” etc. (Gittin 54b), and this is what he writes there:

And one may discuss accordingly whether, if someone rendered his fellow’s pure items impure or libated his wine for idolatry and informed him, but his fellow does not believe him in a case where by law he is not obligated to believe him, because it was not in his power and the like, where the rule that one witness is believed in matters of prohibition does not apply, or where there are two witnesses contradicting him—whether the owner is permitted to derive benefit from his object, since nonetheless the one who admits that he rendered it impure or libated it would be obligated to pay because of a litigant’s own admission, since in truth he did damage the object, only the owners do not know of and do not recognize the damage, and their lack of awareness does not improve the deficiency and loss of the object. And so too this seems, at first glance, from the Ritva in his novellae to tractate Gittin 54b, s.v. “Abaye said,” who wrote as follows: “And that which it teaches, ‘by strict law he is not believed’—regarding one who said, ‘your pure items became impure’—implies that strict law would dictate that he should not be believed, but believed he is, for this is what the wording ‘by strict law’ indicates. One may say that this was stated because of intentional action: where he says that he intentionally rendered them impure or invalidated them, strict law would dictate that he should not be believed, for he is not obligated to pay, since imperceptible damage is involved, and we maintain that it is not considered damage. But now that they enacted that one who acts intentionally must pay, he is believed, for since he is believed regarding himself, he is believed to render them impure or invalid,” see there where he elaborates. And plainly it would seem that ‘since he is believed regarding himself, he is believed to prohibit’ applies only if he is in any event believed regarding himself even if he would not be believed regarding the object. But if the two depend on one another—such that if he is not believed to prohibit, then he too would be exempt—then it is not so fitting to say ‘since he is believed regarding himself,’ for if he is not believed to prohibit, then he is not believed even regarding himself. And it seems from the words of the Ritva that if he says, ‘I rendered it impure,’ he would be obligated to pay even though the owners do not believe him.

From the Ritva’s principle, “since he is believed to obligate himself to pay, he is believed to prohibit,” Rabbi Shimon understands that even if the injured party does not believe the damager, and from his perspective the object remains permitted, the damager would still be obligated to compensate him by virtue of a litigant’s own admission. I can’t understand how Rabbi Shimon inferred this, and the sentence “plainly it would seem that ‘since he is believed regarding himself, he is believed to prohibit’ applies only if he is in any event believed regarding himself even if he would not be believed regarding the object” seemingly makes no sense. After all, he is innovating that although the damager has no credibility in principle—by strict law—through a migo he does have credibility. So what does Rabbi Shimon mean when he says, “that ‘since he is believed… he is believed to prohibit’ applies only if he is in any event believed regarding himself even if he would not be believed regarding the object”? How can it be that he would not be believed regarding the object after this migo was introduced—that since he is believed regarding himself, he is believed regarding the object? That is exactly the whole novelty: that financial credibility grants him credibility regarding prohibition. And how could one fail to believe the words of the damager if the damager is believed regarding himself?
I hope the question is clear and in place, and thank you very much in advance.