# Absense of evidence isn’t evidence of absense

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Why is this the case? Wouldn’t a lack of evidence hint at, but not necessarily prove that this could be the case?

In: Biology

Just because nothing was found doesn’t necessarily mean it’s not there.

I can’t see the stars during the day. That doesn’t mean the stars have disappeared.

So, you’re more right than you’d think.

The reason we say this is because from a formal logical standpoint (where we try to ground debates) it is true – you can never *really* prove that something doesn’t exist, because it’s impossible to look *absolutely everywhere* and categorically rule out it existing anywhere.

But when you look at it from a more probabilistic model, if we’ve been searching for something for a very long time and have been unable to find it, that’s at least some weak evidence that it doesn’t exist (or at least that it doesn’t exist in any sense that we can perceive, in which case it’s like it doesn’t exist).

Let’s say your sister is sleeping in the next room. You can’t hear her snoring or see her sleeping. Just because you can’t hear her snoring doesn’t prove she isn’t sleeping.

Just because you don’t see signs that ninjas are hiding in your room, doesn’t mean that the ninjas aren’t there.

We didn’t have evidence dinosaurs existed, we didn’t have evidence jupiter existed, we didn’t have evidence Japan existed, yet they were all there

I have ten boxes sitting on the table in front of me, and I tell you that one of them contains a valuable gold bar. You’re not entirely sure you believe me. So you open each box and look inside, and you find no gold bars. You now have firm evidence that there isn’t a gold bar.

But let’s say I have 100,000 boxes in front of me and tell you that at least one of them contains a gold bar. There’s absolutely no way you can check every single box for a gold bar. You can check 10 boxes, find no gold bars, and assume that there’s less than a 1:10 chance of any given box to contain a gold bar. You can check 1,000 boxes and assume the chance is less than 1:1,000. But short of opening every single box there’s no way for you to state with certainty that there are *no* gold bars in any of the boxes.

Most things to which your statement apply resemble the latter case (100,000 boxes) more than the former (10 boxes). It’s impossible–or at least infeasible–to examine every single possibility so there’s always a chance, however small, that there’s something there to find. That something might be wildly improbable or uncommon, but that’s not the same thing as impossible or nonexistent.

It does hint at absence, but it still isn’t evidence of absence. Evidence is held to a higher standard than hints.

Just because someone can’t prove that they didn’t eat the pie, is not enough evidence to be sure they did.

The meaning there is pretty clear; if you see smoke, that’s evidence of there being fire, because nothing else causes smoke.

But, what if there’s no smoke? Does that mean there’s no fire? Well, it can mean that, but it isn’t by itself proof. Maybe it’s a clean fire, or it’s a windy day, or maybe you are looking in the wrong direction.

That’s where your expression comes in. It’s a reminder that just because you don’t have evidence of something, isn’t proof that the something isn’t there.

Where it gets tricky is that sometimes absence is evidence, but that’s because it’s linked to something else — “there is no forest fire here And I know that because if these particular treed were burning they’d made smoke” is a very different statement then “there is no fire in town because I don’t see smoke right now.”