Well, to paraphrase a great Republican, here we go again. The details of Adam Lanza’s home environment—the armory of weapons there, the copy of the “NRA Guide to the Basics of Pistol Shooting,” there was a useful book kept close—are scarcely out before the insistence that there’s nothing, absolutely nothing, to see or to do returns, at a higher volume. The President talks, in his calm and conciliatory tones, about minimal gun control—that there’s no threat to responsible gun owners, just common sense—and gets, in return, no response, no counterproposal at all, just the usual toxic cocktail of fatalism and scorn. And he gets contemptuous references to his merely “emotional appeals” on the issue, to his talk, on Thursday, of “shame on us.” As though the horror of children ripped apart by a hundred and fifty-four bullets fired in less than five minutes is not itself rational evidence for change, as though unbearable parental grief is not itself an argument for altering the circumstance that made the mourning happen.

Then there is the “Well, we don’t really know what works!” faction, shrugging off talk of even those minimal measures. You know, there really isn’t much evidence that gun control reduces gun violence. The good and worthy David Brooks—whose role in life, unfortunately, seems to be to try to put a rational face on an irrational political faction—advises in a column that since gun deaths didn’t really end with the last, brief, assault-weapons ban, we shouldn’t press for another, at least not too hard.

Actually, it’s hard to find a more robust correlation in the social sciences than the one between gun laws and gun violence. The cry comes back: “But those are just correlations. They don’t prove causes!” And, indeed, the most recent damning study, published in that cranky, left-wing rag the Journal of the American Medical Association—which shows a clear correlation, state to state, between strong gun laws and less gun violence—ends with the orthodox injunction that the study could not alone determine cause-and-effect relationships, and that further studies are needed.

But when a scientific study ends by stating that there’s uncertainty about whether a correlation proves a cause, it doesn’t mean that correlations are meaningless in every circumstance. Everyone knows that creating false correlations between two unrelated elements is easy. But it can be that a correlation is so powerful and reliable that it may actually point to that rare thing in the social sciences, a demonstrable causal relation. As a wise man once said, “Correlation is not causation, but it sure is a hint.” When you can separate out a truly robust correlation between two elements in our social life, it’s a big deal.

What makes a correlation causal? Well, it should be robust, showing up all over the place, across many states and nations; it should exclude some other correlation that might be causing the same thing; and, ideally, there ought to be some kind of proposed mechanism that would explain why one element affects the other. There’s a strong correlation between vaccines and less childhood disease, for instance, and a simple biological mechanism of induced immunity to explain it. The correlation between gun possession and gun violence—or, alternately, between gun control and stopping gun violence—is one of the most robust that you can find. And the mechanism that connects weak gun laws to gun murders and massacres is self-evident: with guns around, ordinary arguments escalate into ones where someone gets killed, and crazy kids who dream of getting even with the world can easily find a gun—or, like Adam Lanza, many guns—to do it with.

One sign of the robustness of the correlation is that the counterarguments are either easily explodable pseudo-science or stories that people tell each other on Internet forums. “If he’d had a knife, he’d use that!”—well, yes, he would have, and the kids In Newtown would be alive today. In response to real social science, with its cautious but solid correlations, you get obscene, Tarantino-style fantasies—“If the kindergarten teacher had had an assault weapon of her own, loaded, primed, and ready to fire, this wouldn’t have happened!”—and stray tabloid anecdotes—“I heard about this woman, she had a gun, and the marauders just saw it and…” Indeed, that’s the favorite absurdity of the moment: to insist that it doesn’t matter whether or not there’s any evidence that guns are used effectively on any scale in self-defense, because the incidence of gun use doesn’t accurately track the millions of times that the mere sight of a gun in the hands of a housewife scares off the bad guys, causing murderers otherwise determined on mayhem to run away screaming.

Finding a correlation, eliminating a correlation, proposing a correlation—these are not inconclusive fitful stabs at truth: they are meaningful acts. And when you put them together with many other similar, even stronger correlations, a cause stares you in the face and asks you to sit down and take it seriously. To believe that gun laws don’t work, you have to believe that each of the many studies showing that gun laws limit gun violence—all of them, every single one, from Canada to Australia and back home—are not just flawed at the margins or somewhat inconclusive but that they are fundamentally, entirely, completely, round-the-block wrong. And that isn’t a plausible claim.

Common sense confirms what social science correlates. The United States, after all, is hardly the only rich country in the world with laws. American insularity and the ignorance of others is powerful, but it need not be quite so absolute. There are (here we go again!) many countries that resemble ours in wealth and history; they have different gun laws, and they have much lower levels of gun violence. They have about the same incidence of crazy people, but after they have one psycho gun massacre they take action, and then very rarely have another. Meanwhile, the desperately dim efforts to equate some other potentially dangerous thing—cars or trucks or alcohol or airplanes—with guns gets more ridiculous each time they’re attempted. Many good things can have bad consequences in the wrong circumstances. What ought to be done—indeed, exactly what we often do—is to limit the dangerous consequences while allowing for the good ones. That’s why we do things like regulate who drives cars, put warning signs for pregnant women on wine, demand licenses on dogs, check people for box cutters before they board airplanes—all common-sense activities by which we attempt to regulate the risks of our pleasures. (And the Second Amendment has only very recently, and radically, been read as assuring an individual right to guns.)

“But the actual legislation under review is minimal and meaningless!” It’s true: background checks and a bit more enforcement of laws on straw purchases is hardly enough—but (once again) they need to be supported not just as symbols but also because we have learned that any impediment to violence, however low, is better than none at all, and small ones can be surprisingly potent. All kinds of laws help reduce gun violence. As Richard Florida wrote, in a study published in the Atlantic, “Firearm deaths are significantly lower in states with stricter gun control legislation. Though the sample sizes are small, we find substantial negative correlations between firearm deaths and states that ban assault weapons (-.45), require trigger locks (-.42), and mandate safe storage requirements for guns (-.48).” In other words, the mechanism of massacre is simple availability. Any obstacle might spare the life of a six-year-old.