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When question's ask if something exists, and it doesn't - but that's really hard to prove 100% - how does one answer them?

For example, Is there a list of every vessel used in the Beit HaMikdash? - the answer is no, as I explained in a comment (that the is there a list of the 93 vessels used in the temple daily? question got a negative answer.

But there too, how do we prove that such lists don't exist in such rarely learnt location?

So what do we do?

  • Leave it open, with comments? Why?
  • Answer with a no? How long and detailed should the answer be?
  • Close it? Why?
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3 Answers 3

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Mathematical proof is not necessary in answers, and mathematical provability is not a requirement for questions. If a question asks for something that, in fact, doesn't exist, there are three types of answers that I can think of that would productively address the question:

  1. Cite a source that says that the sought item doesn't exist (e.g. here).

  2. Demonstrate why it's unlikely that the sought item could exist (e.g. here).

  3. Describe the extent of your expertise in the matter or efforts to find such an item, demonstrating why the fact that you haven't seen it is good evidence that it's unlikely to exist.

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  • 1
    Exactly what I was thinking... A big +1
    – רבות מחשבות
    Apr 18, 2018 at 15:42
  • 1
    Does an example of # 3 exist? If not, how can you prove it?
    – Alex
    Apr 18, 2018 at 16:01
  • On a more serious note, the weakness of an answer of type # 3 is that the readers still have to rely on an unverifiable premise. That is to say that they have to trust you that you accurately described your expertise or accurately described your research. For instance, I can answer such a question by saying "I've gone through the entire Talmud, and have not found any mention of this". But how do you know that I've actually gone through the entire Talmud?
    – Alex
    Apr 18, 2018 at 16:16
  • @Alex I agree that self-recommendation on an internet forum is not particularly strong evidence. The other two options, if available, are stronger. However, weak evidence is better than none.
    – Isaac Moses Mod
    Apr 18, 2018 at 16:56
  • @IsaacMoses I agree.
    – Alex
    Apr 18, 2018 at 16:57
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When you read the question, what led you to determine that this is a question that falls into the category of "it doesn't exist"? Post that as your answer. Unless it wasn't a good method of determination. But in that case you don't really know that "it doesn't exist" so then the question does not fall into the category you are discussing here.

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Why would a "does this exist?" question be any different than any other question? Whenever you read a question you might be unsure of the answer. Here too you are unsure of the answer. So do what you do in any other case – either don't answer it (but perhaps leave a comment) because you are not sure of the answer, or answer to the extent that your knowledge allows you to answer and include any relevant disclaimers about the incompleteness of the answer.

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