Why Do Arguments Persuade?

Stated that way, this effect can seem commonsensical: of course it’s reasonable for people in such groups to polarize. For example: I see more arguments in favor of gun control; Becca sees more arguments against them. So there’s nothing puzzling about the fact that, years later, we have wound up with radically different opinions about gun control. Right?

Not so fast.

In 2010, Becca and I each knew where we were heading. I knew that I’d be exposed mainly to arguments in favor of gun control, and that she’d be exposed mainly to arguments against it. At that point, we both had fairly non-committal views about gun rights—meaning that I didn’t expect the liberal arguments I’d witness to be more probative than the conservative arguments she’d witness.

This gives us the puzzle. At a certain level of generality, I know nothing about about gun rights now that I didn’t in 2010. Back then, I knew I’d see arguments in favor, but I was not yet persuaded. Now in 2020 I have seen those arguments, and I am persuaded.

Begin with a simple question: why do arguments persuade? You might think that’s a silly question—arguments in favor of gun control provide evidence for the value of gun control, and people respond to evidence; so rational people are predictably convinced by arguments. Right?

Wrong. Arguments in favor of gun control don’t necessarily provide evidence for gun control—it depends on how good the argument is!

When someone presents you with an argument for gun control, the total evidence you get is more than just the facts the argument presents; you also learn that the person was trying to convince you, and so that they were appealing to the most convincing facts they could think of.

Why, then, do arguments for a claim predictably shift opinions about it?

My proposal: by generating asymmetries in ambiguity. They make it so that reasons favoring the claim are less ambiguous—and so easier to recognize—than those telling against it.

Here’s an example about Trump, not gun control.

This is an argument that we should re-elect Trump. Is this a good argument?That is, does it provide some evidence in favor of Trump being re-elected?

​I’m not sure—the evidence is ambiguous. What I am sure of is that if it is a good argument, then it’s so for relatively straightforward reasons: “Trump’s presidency has had and will have good long-term effects.”

If it’s not a good argument, then it’s for relatively subtle reasons: perhaps we should think, “Is that the best they can come up with?”; perhaps we should think that relations with China were already changing before Trump; perhaps we should be unsure whether inflaming the confrontation is a good thing; etc.

Regardless: if it’s a good argument, it’s easier to recognize as such than if it’s a bad argument As a result, we can expect to be, on average, somewhat persuaded by arguments like this.

As before, it’s entirely possible for this to be so and yet for the argument to satisfy the value of evidence—and, therefore, for us to expect that it’ll make us more accurate to listen to the argument rather than ignore it. At each instant we’re given the option to listen to a new argument or not, we should take it if we want to make our beliefs accurate.

And yet, because each argument is predictably (somewhat) persuasive, long periods of exposure to pro (con) arguments can lead to predictable, profound, but rational shifts in opinions.

We can model how this worked with me and Becca. The blue group (me and my liberal friends) were exposed to arguments favoring gun control—that is, arguments that were less ambiguous when they supported gun control than when they told against it. The red group (Becca and her conservative friends) were exposed to arguments disfavoring gun control—that is, arguments that were more ambiguous when they supported gun control than when they told against it.

Suppose that, as a matter of fact, 50% of the arguments point in each direction. Because of the asymmetries in our ability to recognize which arguments are good and which are bad, the result is polarization:

Upshot: it is not irrational to be predictably persuaded by (ambiguous) arguments; yet the more people separate into like-minded groups, the more this leads to polarization.

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