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There's a common principle found in various academic disciplines, that absence of proof does not equal proof of absence (ie: a lack of evidence for something doesn't mean that it does not exist). I am often reminded of Eduyos 2:2 and Zevachim 12:4, in which the chakhomim tell Rabbi Akiva that "אין לא ראינו ראיה" ("We did not see it" is not a proof).

Given, however, that the chakhomim had to say this to Rabbi Akiva, and given that he did just use it as a proof, does that mean that Rabbi Akiva didn't hold to this principle?

Did Rabbi Akiva believe that not ever having seen something accounted to an argument in favour of that thing's non-existence?

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  1. Absence of proof is not proof of absence, but it is a strong indicator of absence
  2. The degree to which "לא ראינו" is an indication of absence depends on the size of the domain. If we are dealing with the whole planet as the domain, but our area of observation is only our local vicinity, then absence of proof is a very poor indicator for the whole domain. If our area of observation covers the full domain, then it is a strong indication of absence, but still not a proof.
  3. Rabi Chanina's observation covered many years of Temple activity, which was the relevant domain. His lack of observation was a very strong indicator that the non-observed behavior was halachically precluded, and that is why he did not observe it.
  4. Halachically we rarely require proof, we only need a strong indication ("חזקה", or related concepts). Even two witnesses is far from being a proof, but it is accepted absolutely.

R' Akiva believed that the "לא ראינו" of Rabbi Chanina was sufficient to be a halachic basis for determining that it was a matter of law, while the Chachamim argued that it was not an acceptable basis even as an indicator of likelihood.

  • It can be a strong indicator of absence, or not, based on context—i.e. how unlikely it would be for there to be no evidence despite the alleged thing actually existing. There are many things for which we have not found evidence, but since we expect the evidence for those things to be hard to find or easily missed or whatever else, this absence of evidence is not seen as a strong indicator of absence, since we accept that we could very easily have such an absence despite the phenomenon actually existing. Your second point gets into this, but the first should perhaps be “can be” instead of “is.” – KRyan Jul 7 at 17:54
  • @KRyan A perfect example are solar neutrinos. There are MANY of them they are all around us, yet it is incredibly difficult to observe them thus it took until 2014 to confirm them. – DRF Jul 8 at 7:16
  • Fair points, but this is really aquestion if we even have a "absence of proof" in the first place. If someone with no relevant observations (I have never seen a Martian") concludes that something does not exist (there are no Martians) the problem is not a fallacy of "argument from ignorance", it is that they have no relevant information at all. If there are limited opportunities for observation then obviously non-observation does not give any indication of non-existence, because there is no information at all. – simyou Jul 8 at 7:50

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