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Most of what you're saying is right, but the saying isn't nonsense. It's just describing the problem that comes up when you can't find evidence of something. If
by ewzimm 10y ago
Most of what you're saying is right, but the saying isn't nonsense. It's just describing the problem that comes up when you can't find evidence of something. If its presence would necessarily present evidence, as with the gorilla (unless it's a mutant ninja gorilla), then it's evidence of absence. If its presence would not necessarily present any detectable evidence, then it's absence of evidence, meaning that you haven't really learned anything. With something like aliens, we don't actually know what evidence to look for, so as you're saying, there's no evidence of absence yet, only absence of evidence.
- mikeash 10y agoIt is nonsense, because the saying is absolute. It doesn't say "absence of evidence is not necessarily evidence of absence." In reality, evidence of absence sometimes is and sometimes isn't evidence of absence, it depends on the specifics. The fact that the saying is correct for some cases doesn't make it sensible, any more than saying "birds don't fly" is sensible because of penguins and ostriches.
- ewzimm 10y agoIt's just a cute aphorism that describes one of the main challenges in science. The "is not" is meant to convey that there are two distinct conclusions that we can make from seeing a lack of something and that it's important not to make the wrong choice while evaluating the situation. We can't automatically say "absence of evidence" or "evidence of absence" as it suits our preconceptions but need to look deeper into why something is missing.
- mikeash 10y agoWell, every single time I've seen someone use that phrase, it hasn't been to point out that they're not equivalent, it's been to argue for the potential existence of something where there's zero evidence for it and lots of searching you'd expect to turn up evidence. Case in point here, we are not discussing aliens in general, where that phrase might be sensible, but rather aliens frequently visiting Earth over a period of years in the form of UFOs.
- ewzimm 10y agoIt can absolutely be abused, but that really just proves the point of the statement, that people tend to make biased and wrong decisions when they don't apply thorough logic. For clarity, it could have been "absence of evidence is not sufficient evidence of absence," but it just doesn't sound as nice. But it in that form and how it's intended by logicians, it's perfectly valid.
- mikeash 10y agoMy point is that it is never anything but abused. Does a statement really have a point that's independent from how people use it? Especially when that use agrees with the statement's literal meaning?
- ewzimm 10y agoThis seems like a case where something completely legitimate got so abused that it lost its meaning to many people. It does have a point. It's a classic phrase used in teaching logic to rebut the logical fallacy of an argument from ignorance. I think what you've seen is a lot of people using the authority of something from formal logic to back up their own fallacious arguments. "The phrase "the absence of evidence is not the evidence of absence" can be used as a shorthand rebuttal to the second form of the ignorance fallacy (i.e. P has never been absolutely proven and is therefore certainly false). Most often it is directed at any conclusion derived from null results in an experiment or from the non-detection of something. In other words, where one researcher may say their experiment suggests evidence of absence, another researcher might argue that the experiment failed to detect a phenomenon for other reasons." https://en.m.wikipedia.org/wiki/Argument_from_ignorance https://en.m.wikipedia.org/wiki/Argument_from_ignorance