All right, I’ve been meaning to do this post for a while now, and since it’s come up again in my personal life, I think it’s about time.
Very frequently, when I’ve been present on blogs and forums debating about the existence of one thing or another, a common proverb is set forth: “Absence of evidence is not evidence of absence.” On the face of it, this sounds good. I can’t sense something, for instance, living in my walls, but that doesn’t mean there definitely isn’t something living in my walls. I’d be silly to say, “There’s nothing in there,” right?
Let’s try a little experiment. Look around the room you’re in right now, closely. No, this isn’t a thought exercise, quit reading and look.
Back now? Good. How many Peruvian alpacas did you see? None? I’m surprised, but okay. So you’re comfortable with saying there’s no Peruvian alpacas in the room? Aha! Absence of evidence is not evidence of absence! You can’t definitively say there’s no alpacas in the room!
Yes, it’s a damn silly argument. Evidence for certain distinct things is readily detectable, and the parameters for their existence can rule out, for instance, alpacas hiding under a stack or papers or behind the bookshelf. In fact, you’re comfortable with saying that there are no alpacas in the room only because of the lack of evidence.
So we’ve proven that proverb wrong? Good. You’ll find that you can do this with damn near every proverb you can find. Don’t think in proverbs – they’re crutches on proper thinking. And don’t fall for them. They’re quite often intended to sway arguments through popularity, brevity, and the bias we have towards quick and simple solutions. In fact, when someone spouts a proverb or cute saying at you, it’s a good habit to immediately stop and think if this is an attempt to get you to fall for bullshit.
If you haven’t already (numerous times,) at some point in your life you’ll have someone challenge you to proving a negative. This one is so prevalent I’m liable to start harassing grade-school teachers to include it in their lesson plan. How do you prove a negative? You don’t – you can only establish a lack of evidence for it. But even establishing a lack of evidence can be a ridiculous task, depending on the nature of the subject you’re debating. The alpaca above is easy – they’re fairly big, noisy, smelly, and tend not to hold very still in the closet. But, for instance, extra-terrestrial life? Cold fusion? You’d be attempting to show what the entire universe contains to demonstrate the lack of evidence. Which is the only reason you’ll find this tactic is used at all.
We, however, operate on a basic assumption. You’ve almost certainly heard some saying about making assumptions, and now I’m going to spike that one too. The basic assumption is, it doesn’t exist until some evidence has been established that it can exist. Flying purple wombats? Space trees 4,000 light years tall? Invisible rocks? If I told you I believe in them, you’d think I was wobbly. And, you’d be right. You’d at least be perfectly within your rational mind to say, “Show me.”
Even scientists that deal with theoretical particles and astronomical bodies are careful to show how the physical laws that we use every day can extend out to support the idea of their theory. Now, here’s the kicker: They don’t ever say they’ve proven it. Black holes, for instance, were first worked out on paper in ridiculous amounts of math, based on General Relativity. Einstein, who formulated the theory of General Relativity, admitted to not actually liking the idea of black holes, of something so gravitationally strong that it would collapse into a singularity. And, he also admitted the math showed no flaws. Over the years, the theory of black holes has been gone over by countless astrophysicists and refined but again, never discarded due to flaws. And now, with the discovery of certain kinds of radiation in prime circumstances for their formation, black holes are considered better than 90% certain. But not “proven.”
What’s funny is, at certain times you may be expected to formulate your thoughts in terms like this – probabilities, but not definitive statements. First off, this can be extended to anything at all in our base of knowledge, thermodynamics for instance. Can you prove that the pot on the stove will absorb heat from the burner beneath it? No, actually I don’t ever worry about it until it fails.
There have been numerous things that I have challenged the existence of to the people who promote them, and when pointing out the lack of evidence, I have been told I haven’t disproven them. I haven’t disproved [SPOILER ALERT] Santa Claus either, but I have no issues whatsoever with saying he does not exist. I’ll be more than happy to retract that, too – once someone actually delivers some nice, clean evidence. Until that time, I’m fine with relegating Santa, Bigfoot, extra-terrestrial intelligent life, and great-tasting diet food to the bin of “doesn’t exist.” Call it a shortcut if you want – if we treated everything we ever do or discuss in terms of probability, our conversations would get pretty annoying.
The thing is, there is no actual difference between “Chupacabra does not exist” and “There is no evidence for Chupacabra.” You may get challenged on making a definitive statement, but correcting this for scientific accuracy does not advance the argument. It simply means that your opponent is desperate for an opening, anything that can present a crack to wedge their argument into. In some cases, your opponent may want to establish that you’re not providing a dismissive answer automatically, such as, “All baseball players suck.” But basically, who cares? The onus still remains on them to provide positive evidence, regardless of whether their debate opponent is dismissive or extremely fair.
Another example: Gnomes do not exist, therefore there is no evidence for gnomes. Hard to argue, right? Reverse it: There is no evidence for gnomes, therefore gnomes do not exist. Ah, that’s not necessarily the case! True, but so what? Such an argument is about logic within the statement, not about establishing the viability of gnomes. Even a grossly illogical statement does not admit to the existence of gnomes by default. If gnomes do not exist, the latter example above, while not logical, still reaches the correct result. Whoops! Relying on logical equations doesn’t solve our problems.
Stick with positive evidence, and remember that proof is an abstract. And don’t let yourself fall for the negative proof or logical statement fallacies.