On falsifiability and the null hypothesis in discussions and debates.
tl;dr: If you’re debating with someone, it is always important to decide in advance, what proof or situation would be needed for either of you to change your mind. If no possible proof can ever do that, you wouldn’t be having a discussion, you’d be blindly arguing to prove a point.
In experimental science, when creating a research protocol for an experiment, we have to define a null hypothesis and then disprove it to prove the experimental hypothesis we are testing. This is closely linked to the notion of falsifiability as defined by Karl Popper. Falsifiability means that in order to study something, we should at least be able to imagine a scenario or a result in which what we are trying to prove can be wrong. I’ll give my favorite example that explains the problem with non-falsifiability as written by Carl Sagan (excerpt from “The dragon in my garage”):
“A fire-breathing dragon lives in my garage”. Suppose I seriously make such an assertion to you. Surely you’d want to check it out, see for yourself. There have been innumerable stories of dragons over the centuries, but no real evidence. What an opportunity! “Show me,” you say. I lead you to my garage. You look inside and see a ladder, empty paint cans, an old tricycle — but no dragon. “Where’s the dragon?” you ask. “Oh, she’s right here,” I reply, waving vaguely. “I neglected to mention that she’s an invisible dragon.” You propose spreading flour on the floor of the garage to capture the dragon’s footprints. “Good idea,” I say, “but this dragon floats in the air.” Then you’ll use an infrared sensor to detect the invisible fire. “Good idea, but the invisible fire is also heatless.” You’ll spray-paint the dragon and make her visible. “Good idea, but she’s an incorporeal dragon and the paint won’t stick.” And so on. I counter every physical test you propose with a special explanation of why it won’t work.
And this can go on and go on, for every counter-argument you give, Sagan will come up with a new condition to invalidate it. In this scenario, you can never disprove Sagan’s claim of having a dragon in his garage. However, your inability to invalidate his claim does not mean that his claim is true. The burden of proof is on him (we’ll try to write something on the burden of proof in another post).
Another example of a non-falsifiable topic from everyday life is astrology, that is still printed in most newspapers. Astrology and other “fortune teller” usually word their predictions in such a vague way that they can never be wrong and are thus non-falsifiable (Forer effect). Debate as much as you want with a person that believes in horoscopes and chances are that they will always add a new condition in which the horoscope prediction stands.
Conversely, we can imagine falsifiable claims: in 2017, Pluto is going to implode. This is quite a falsifiable statement, we can imagine a scenario where we can test this claim: we wait for 2017 to pass by and if Pluto doesn’t implode, then the hypothesis is wrong.
When having discussions (online or not), it is very important to decide what it would take to prove the claim one is making to be false. If you are debating any subject of discussion from the most mundane to the most crucial; whether it’s someone that doesn’t believe in evolution or another that believes that their girlfriend is cheating on them ; ask them: what would it take for you to change your mind? What should I present to have you doubt your belief?
If under no scenario can one come up with a set of conditions under which they would reconsider their point of view, then the discussion isn’t a discussion but rather a pleading to be right like a lawyer that would say anything to prove his point in court.
Always define your premises and falsifiability criteria before starting a debate or a though-experiment. This would allow you to avoid -at least some- pointless erring that would just end up with each of you discarding whatever the other person is saying because, by design, any other outcome is impossible.