There is a lot of news today about what the swine flu epidemic could do. Influenza — with the right mutations — could kill millions of people. It’s done it before and we are not yet quite able to stop an epidemic dead in its tracks. So, it could be bad. But, saying that is different from saying it will be bad. Scientists use these words fairly carefully, usually, but the world doesn’t always read them with the same intent with which they were written.
So, what does “could” mean to a scientist? Well, the opposite is “couldn’t”. You’ll almost never see a properly cautious scientist saying “an epidemic couldn’t happen.” The word “couldn’t” means “never”, “nada”, “impossible”, “not in a billion years”. So, “could” gets used a lot and it doesn’t mean much. I’ll try to write a few sentences with the word “couldn’t”, but it’s very hard — I feel the need to add some qualifications after each one to stay properly honest:
- The Earth cannot just explode. (This one I’m fairly happy with. I mean, you could probably find a good astrophysicist who would cook up a way for it to happen involving billions of years and Dark Energy, or perhaps colliding quantum black holes, but…)
- You cannot mutate into a frog. (OK, maybe you could if every cell in your body were simultaneously hit by a cosmic ray, and if every one of the billions of individual mutations were exactly right. But, it is a really, really safe bet that it will not happen in the lifetime of this universe.)
- No human will ever travel faster than the speed of light. (Well, not unless someone comes up with some pretty surprising new physics, anyway. There are a lot of experiments that support Einstein and Relativity…)
If I were to say “couldn’t”, in a scientific capacity, I’d have to bite my tongue to avoid adding one of those little parenthetical quibbles after it. And those bulletted sentences above are much more certain than statemens about epidemics. We still know darn little about epidemics, even if we know a lot more than we did a decade ago. So, if you’re a scientist, and some reporter asks “Could this kill us all horribly?” it is very hard not to answer “yes” (unless you can prove otherwise). After all, you think you’re answering his question honestly and cautiously. Then, the reporter takes “could” and treats it as a big chance rather than a small chance. The trouble is really a cultural thing. Admittedly, both the reporter and the scientist are looking for some good publicity, but the important thing is that they come at the word “could” from different sides.
Even if you know a little bit about human nature and try to play it safe, it’s hard to avoid saying “Of course it could, but it’s not very likely…” That’s almost as bad. To the reporter, you agree up front; it is all too easy for him or her to trim off the tail. To the scientist, the “Of course it could” is weak. It is the default. It almost goes without saying. But to the reporter, that is the center of the quote.
What you really have to do, if someone asks you the “could it?” question is act like a politician. Don’t answer the question that was asked. Instead, answer the question that the reporter should have asked. But that’s hard. We’re trained to answer. It’s also hard to think on your feet, put yourself in the reporter’s shoes and figure out the right question to answer. Especially if the right question has an answer that’s a little more complex than will fit into a news story. Or, especially if we don’t really know the answer.