I agree with you that Zvi and Eliezer are both correct, but I am unconvinced by your analysis of why. I don’t think “no evidence” is vague. I think it’s false.
“There is no evidence of Bigfoot” is simply untrue. There are people who claim to have seen things-that-maybe-could-be-Bigfoot. There are people who claim to have found footprints and the like. All these things are evidence. Crappy evidence, which is why it doesn’t do much to change my opinion that Bigfoot is almost certainly not real, but still evidence.
“Nobody looked for Bigfoot and nobody found him” is also evidence that Bigfoot doesn’t exist. (There are possible worlds in which Bigfoot gets seen by people who weren’t actively looking. If nobody looked and nobody found, those worlds are ruled out.)
So, when someone says “there is no evidence of Bigfoot”, what they are saying is not literally true, and they almost certainly know it, and that’s evidence of bullshit or, at best, thinking sloppy enough that they might as well be bullshitting.
We can get back to something like your complaint of vagueness if we apply a bit of extra charity and suppose that when they say “there is no evidence of Bigfoot” they mean something like “there are no pieces of evidence of Bigfoot that are individually very strong evidence”. In that case, there are two possible charges of vagueness we could bring:
It could mean “there are no photos that are unquestionably of Bigfoot”, or it could mean “there are no credible eyewitness reports”, or it could mean “there are no videos”, etc. I don’t really buy this criticism; I think it’s fairly clear that the meaning is pretty much what I said above.
Having decided what it means, it then potentially matters a lot what things have been going on that one might expect to produce such evidence. As you say, having no photos, eyewitness reports, etc., is stronger evidence if lots of people have been out looking hard than if no one has been.
But I don’t think this situation is accurately described by saying that the statement is vague. It’s just a fact of life that sometimes the conclusions we should draw from an observation depend on its context.
If someone says, in so many words, “To the best of my knowledge, no one has ever presented any piece of evidence for Bigfoot that a reasonable person would find compelling”, I don’t think I could reasonably complain that they’re being vague or bullshitty, even though what I’d conclude would depend on how hard I thought people had been looking for such evidence.
I disagree. Much of what’s going wrong is differing meanings of the word evidence.
Most people are oblivious to the Bayesian meaning of the word evidence. When I hear an ordinary person say “no evidence”, I usually interpret it as “no evidence that’s admissible in a court”, or maybe even “no proof”.
I agree with you that Zvi and Eliezer are both correct, but I am unconvinced by your analysis of why. I don’t think “no evidence” is vague. I think it’s false.
“There is no evidence of Bigfoot” is simply untrue. There are people who claim to have seen things-that-maybe-could-be-Bigfoot. There are people who claim to have found footprints and the like. All these things are evidence. Crappy evidence, which is why it doesn’t do much to change my opinion that Bigfoot is almost certainly not real, but still evidence.
“Nobody looked for Bigfoot and nobody found him” is also evidence that Bigfoot doesn’t exist. (There are possible worlds in which Bigfoot gets seen by people who weren’t actively looking. If nobody looked and nobody found, those worlds are ruled out.)
So, when someone says “there is no evidence of Bigfoot”, what they are saying is not literally true, and they almost certainly know it, and that’s evidence of bullshit or, at best, thinking sloppy enough that they might as well be bullshitting.
We can get back to something like your complaint of vagueness if we apply a bit of extra charity and suppose that when they say “there is no evidence of Bigfoot” they mean something like “there are no pieces of evidence of Bigfoot that are individually very strong evidence”. In that case, there are two possible charges of vagueness we could bring:
It could mean “there are no photos that are unquestionably of Bigfoot”, or it could mean “there are no credible eyewitness reports”, or it could mean “there are no videos”, etc. I don’t really buy this criticism; I think it’s fairly clear that the meaning is pretty much what I said above.
Having decided what it means, it then potentially matters a lot what things have been going on that one might expect to produce such evidence. As you say, having no photos, eyewitness reports, etc., is stronger evidence if lots of people have been out looking hard than if no one has been.
But I don’t think this situation is accurately described by saying that the statement is vague. It’s just a fact of life that sometimes the conclusions we should draw from an observation depend on its context.
If someone says, in so many words, “To the best of my knowledge, no one has ever presented any piece of evidence for Bigfoot that a reasonable person would find compelling”, I don’t think I could reasonably complain that they’re being vague or bullshitty, even though what I’d conclude would depend on how hard I thought people had been looking for such evidence.
I disagree. Much of what’s going wrong is differing meanings of the word evidence.
Most people are oblivious to the Bayesian meaning of the word evidence. When I hear an ordinary person say “no evidence”, I usually interpret it as “no evidence that’s admissible in a court”, or maybe even “no proof”.