Yesterday, Neil DeGrasse Tyson, the famous astrophysicist and advocate for better and more rigorous science communication, tweeted this:
It’s hard to fit nuance into tweets, of course, and people have gotten themselves into a lot of trouble by trying to make big, complicated points on a platform not suited to them. But in this case, the specificity of the tweet suggests Tyson really does think an idea like this could work, that all you need to know about the proper relationships between evidence and public policy can be summed up in one line: “All policy shall be based on the weight of evidence.”
It sounds great! After all, we are awash in policies that are weightless, evidence-wise. We’ve elected to powerful positions a bunch of people who don’t believe human-caused global warming is a thing. For decades, we’ve harshly punished drug users who need treatment, despite the overwhelming lack of evidence this approach works. And on and on and on — there are countless examples. There’s more than a kernel of truth here.
But the most common reaction to Tyson’s tweet, as least from what I can see, hasn’t been Right on! It’s been closer to That is a pretty dumb tweet. And it is, in fact, a pretty dumb tweet — uncharacteristically so, given how smart the author is — but one which usefully sums up a common misconception held by folks who bang the drum loudest for science and reason.
Science and reason are great, of course, and in every case it’s better for our policies to be guided by these principles than, say, adherence to old religious texts or to the whimsy of an unelected king. But that the idea of proof is easily defined is where things get tricky. Basically any complicated policy question involves tradeoffs, and when it comes to tradeoffs, there’s no such thing as the logic-driven “right” answer. You need to invoke values, and people will always argue over values because they always have.
David Roberts made this point nicely in Vox: Okay, he said, let’s say we’re in Rationalia. How do we handle global warming? How should we weigh damage which will occur 25 years from now as compared to damage which will occur five years from now? How should we handle issues pertaining to which nations should chip in the most to cleanup efforts, and which nations will be most devastated by rising ocean levels and so forth? How should we weigh the probabilities inherent in climate modeling when we figure out which policies to choose?
“I look forward to hearing what the weight of evidence has to say on these matters,” writes Roberts at the end of his post. The subtext is clear: These questions can’t be answered definitively by pointing to cold, hard, evidence. Values come in, and Tyson’s nifty one-line constitution doesn’t have anything to say about values.
Don’t take this as an argument that reason and evidence are worthless — they aren’t, of course. On the biggest questions — Is evolution real? Is climate change? — there are clear and unequivocal answers, and those answers, yes, are guided by boatloads of evidence, and values don’t come into the equation much. But as soon as you drill down to the level of attempting to find actual, real-world solutions to complex problems, as soon as you gather a thousand nerdy scientists in a conference hall ready to hammer out What Must Be Done, a gaggle of competing values bulldoze past security and crash in, drunk and bickering and ranting and spilling stuff everywhere, messing up what was supposed to be a dignified and straightforward affair. Happens every time.