Mill's Trident is Blunt

Why "Free Speech Warriors" need sharper tools

I mostly intend to avoid writing about hot button issues in contemporary politics on this Substack. First, because lots of other people are talking about them, it’s hard to say anything distinctive. And second, talking about politics tends to bring out the worst in us, myself included. Plenty of people who are careful, subtle, and charitable when writing about Kant or music or quantum mechanics become simplistic and Manichean when the topic turns to politics.¹ They rigorously scrutinize evidence that purports to undermine their convictions, while breezily endorsing sloppy arguments for conclusions they agree with. Statements from opponents are inspected for unsavory associations, while statements from allies are read as charitably as possible. These temptations exist for everyone, and the easiest way to avoid them is to stick to topics that don’t get our hackles up, where it doesn’t feel like the potential answers to the questions we pose already come associated with one or another political team.

So mostly that’s what I’ll do. But when I do write on politics, here’s how I’ll attempt to avoid these common pitfalls. I’ll try to limit myself to friendly fire; I’ll raise problems for views that I’m largely sympathetic to, rather than attacking positions I think are thoroughly misguided. I’ll focus on the planks in my eye, rather than the specks in others’. Instead of preaching to the choir, I’ll ask whether they’re singing off-key.

Today, my topic will be an argument called “Mill’s Trident”. Here’s how Greg Lukianoff, president and CEO of FIRE, summarizes it:

There are only three possibilities in any given argument:

1. You are wrong, in which case freedom of speech is essential to allow people to correct you.

2. You are partially correct, in which case you need free speech and contrary viewpoints to help you get a more precise understanding of what the truth really is.

3. You are 100% correct, in the unlikely event that you are 100% correct, you still need people to argue with you, to try to contradict you, and to try to prove you wrong. Why? Because if you never have to defend your points of view, there is a very good chance you don’t really understand them, and that you hold them the same way you would hold a prejudice or superstition. It’s only through arguing with contrary viewpoints that you come to understand why what you believe is true.

Most of the times I see this kind of reasoning deployed, I agree with the position it’s being used to defend. One of the first things I did after getting tenure was sign up as a member of Heterodox Academy. A few years letter, I was happy to add my name to a letter encouraging, among other things, “activities on campus intended to foster greater tolerance for diverse points of view.” As a materialist atheist, I co-taught a class on issues in the philosophy of religion with Ross Douthat, who thinks everyone should be religious, and in admitting students to the class we prioritized having a wide variety of religious and non-religious views represented. I’m trying to establish my bonafides as someone who is very much a supporter of dialogue across disagreement, and for whom a broadly Millian attitude towards free speech, open inquiry, and viewpoint diversity feels deeply correct.

That said, I think abstract, content-neutral arguments about these values—arguments like Mill’s trident—can’t get us all that far. In particular, in contexts where the question isn’t merely about permitting inquiry, but supporting it—with government grants, tenure track professorships, and the like—it’s impossible for all views to be equally supported, and anyone allocating limited resources needs to make substantive decisions about which projects are the most promising. In such contexts, Mill’s trident is blunt.²

That’s where I’m going. But I’ll take a detour via Karl Popper’s philosophy of science. I’ll argue that some familiar problems for Popper’s philosophy of science closely parallel problems for Mill’s trident.

Popper

Philosophers love to hate Karl Popper.³ Why? Certainly part of it is jealousy. Plenty of philosophers have science envy, and scientists love Karl Popper.⁴ But scientists also love Einstein, and philosophers love to love Einstein. Philosophers love to hate Popper because they think he’s undeservedly popular. Why would they think that?

Popper is mostly known among the public for his view that what’s important about science is falsifiability. A good scientist makes concrete claims that risk being proved wrong, rather than hiding in the refuge of unfalsifiable pseudoscience. In my view, this is a fundamentally sound idea, but it’s not really all that distinctive to Popper—plenty of other contemporaneous writers in the positivist tradition had similar views about the importance of making empirical claims that could be tested by observation.⁵ What’s truly unique to Popper among recent philosophers of science are his views about induction: the practice of extrapolating from past observations to predictions about the future.

Hume famously raised deep skeptical puzzles about induction. In a very small nutshell, he argued that it was impossible to offer a compelling, non-circular defense of the practice.⁶ Most people who encounter Hume’s discussion of induction see it as a paradox to be resolved. Kant famously called it a “scandal” that philosophy as yet had no satisfying response to Hume’s skeptical challenges. But not Popper. He thought the straightforward, skeptical lesson of Hume’s discussion was just correct. There really is no good answer to Hume’s problem of induction: observations of the past give us no reason to form beliefs—not even tentative, probabilistic guesses—about what the future will be like. So we should interpret scientific practice in such a way that it doesn’t involve doing anything of the sort. I know this sounds crazy. But he’s pretty explicit. Here’s a representative quote from the preface to Conjectures and Refutations:

The way in which knowledge progresses, and especially our scientific knowledge, is by unjustified (and unjustifiable) anticipations, by guesses, by tentative solutions to our problems, by conjectures. These conjectures are controlled by criticism; that is, by attempted refutations, which include severely critical tests. They may survive these tests; but they can never be positively justified: they can neither be established as certainly true nor even as 'probable'

So if scientists aren’t trying to show that their conjectures are true, or even probable, what are they trying to do? They’re not trying to verify or confirm, but only to falsify. The best case scenario is that a conjecture has survived many tests—it has withstood repeated attempts at falsification. But even then, we don’t get to believe it’s any more likely to be true.

There are lots of reasons to find this view absurd, but I’ll focus on just one. An important aspect of scientific practice is that scientists try to test theories in novel ways. They build giant, multibillion-dollar particle accelerators so they can smash stuff together harder and faster than ever before, in the hopes of getting new insights into the fundamental fabric of the cosmos. But that only makes sense against the background assumption that we need to spend all that money devising novel experiments because rerunning old, familiar experiments would be uninformative. If you want to test general relativity, why not just keep dropping a ball in your lab, measuring the fall each time? On Popper’s view, it’s hard to see why that’s not just as good a test as what we’d get from observations of previously unseen distant galaxies; both provide opportunities for falsification.

The reason we don’t keep dropping the ball is because we already know what we’ll see if we do so. By contrast, we don’t already know what we’ll see when we build the new particle accelerator or space telescope. Or, if you prefer to think about our beliefs in degrees, at least grant that we are nearly certain what will happen when we drop the ball over and over, while we are highly uncertain what we might learn from novel sources of evidence. The potential for resolving that uncertainty is why we value novel experiments, and the lack of uncertainty to be resolved is why we’re uninterested in rerunning old experiments. But on Popper’s view, we know nothing about the future—we don’t even get to assign probabilities. And so it’s hard to see what rationale there could be for prioritizing new sources of evidence over old ones. Yet clearly that’s what scientists do, and rightly so.

Mill

Popper’s error amounts to imagining scientists as more humble and open-minded than they really are or ought to be.⁷ Mill’s trident involves a similar mistake. Just as Popper’s view of science becomes hard to square with how scientists actually behave, so too Mill’s defense of free speech starts to look questionable once we notice that good thinkers, like good scientists, eventually shift their attention away from the already-settled. The parallel is this: Popper’s view implies we never get to be confident about what we’ll see when we rerun old experiments, so we have no reason to do new experiments. Mill’s Trident—the third prong in particular—implies we never get to rationally disregard a viewpoint, so we have no reason to stop engaging with it. In both cases, there’s no license to move on.

But of course we do move on. Scientists stop re-running the same experiment once they’re confident what the results will be, and shift their attention to more uncertain areas. Similarly, thinkers and institutions stop engaging some arguments—not because they’ve been censored, but because they’ve been settled. That’s not always a mistake. Sometimes, the Overton window narrows for bad reasons. But sometimes it narrows for good ones—for reasons that are themselves the product of open inquiry, evidence, and debate.

This argument is difficult to make for philosophers, who are temperamentally averse to treating anything as settled. Aristotle proposed the law of non-contradiction over two thousand years ago, but there are well respected philosophers today who argue that some contradictions are true. If we can’t treat basic laws of logic as settled, there’s little hope we’ll agree on much else. But not all disciplines are philosophy, and thank goodness for that. What’s the point of all this searching for truth if we never get to decide—at least provisionally—that we’ve found it?

If Mill’s trident shows anything, it is that there’s always some possible benefit from engaging an argument you disagree with, even if you’re sure it’s wrong. But that’s a very weak claim. There’s also some possible benefit from dropping a ball and measuring its rate of descent, just in case this time it falls faster than current physics says it should. But in both cases, if there’s anything else you might be doing with your time—if you have limited resources to devote to your inquiries—you might reasonably decide that slight chance of benefit is not worth it.

So What?

Arguments like the ones I’ve just offered can be misused. They’re often deployed to deflect concerns about ideological homogeneity: “Sure, we don’t have any creationists in the department of ecology and evolutionary biology, or flat earthers in the department of geology, or holocaust deniers in the history department, but that’s fine: not every argument is worth engaging.” Fair enough. We shouldn’t demand that every view be institutionally represented, regardless of its merits.

But that concession shouldn’t be the end of the discussion. It should be the beginning. If you think the narrowing of academic debate is a problem, you can’t just point to the fact that some views aren’t represented; you need to make a targeted case that we’d be better off spending more of our intellectual energy discussing the views you worry we’re missing. But the same goes for defenders of the status quo. It’s not enough to note that some views are beyond the pale and gesture vaguely at crackpots and bigots. If you think we haven’t lost much by marginalizing certain kinds of dissent, then you too need to make a substantive case: that the views in question are sufficiently implausible or intellectually barren that there’s little to be learned from engaging them. As it turns out, I think that in plenty of parts of academia there’s a powerful case to be made that we need more political diversity; we’re missing out on perspectives that are not relevantly similar to holocaust denial, and our research suffers for it.⁸ But the case will always turn on a series of messy, contestable claims, with no knockdown arguments or silver bullets to be had. No wonder so many people prefer to stick to the more comfortable realm of abstract principle.

1. What’s my evidence for this? My Facebook page.

2. When it comes to questions about what speech the government should allow, I’m much closer to a pure proceduralist. I think American first amendment jurisprudence—with its broad prohibitions on content-based restrictions on speech, and only narrow, circumscribed exceptions to those prohibitions—is pretty great.

Moreover, I think first amendment jurisprudence is a good model for universities, so even though private universities can adopt restrictions on speech that wouldn’t pass first amendment muster, I agree with FIRE in thinking that they generally shouldn’t.

3. “Hate” is too strong, Popper was brilliant, I know I know. Don’t @ me.

4. Not all of them, of course.

5. In an alternate history where Rudolf Carnap occupied the role in the public imagination that Karl Popper does, I think far fewer philosophers would be complaining.

6. I give an introductory primer on Hume on induction in amusingly illustrated videos here and here.

7. This is not a novel criticism. Kuhn famously emphasized against Popper how scientific practice involves taking a lot for granted, and rightly so.

8. For a flavor of how the case might go in psychology, see here.