When it comes to the “Arms” protected by the Second Amendment, the conceptual space is typically divided into two categories. Some weapons, like those that are “dangerous and unusual,” can be banned without raising any constitutional problems. For those that are not dangerous and unusual, the government has to satisfy some requisite level of scrutiny. But—and I hate to do this again, having just made a conceptually similar argument about the Two Part test—there also seems to be a third category: Weapons that cannot be banned without categorically violating the Second Amendment.

Heller itself provides a ready example. The Court there applied no particular form of means-end scrutiny, instead writing that DC’s “handgun ban amounts to a prohibition of an entire class of ‘arms’ that is overwhelmingly chosen by American society for that lawful purpose.” The Court concluded that handguns have a unique relationship to the core Second Amendment interest in self-defense, and no prohibition on them can be justified:

It is no answer to say, as petitioners do, that it is permissible to ban the possession of handguns so long as the possession of other firearms (i.e., long guns) is allowed. It is enough to note, as we have observed, that the American people have considered the handgun to be the quintessential self-defense weapon. . . . Whatever the reason, handguns are the most popular weapon chosen by Americans for self-defense in the home, and a complete prohibition of their use is invalid.

The availability of other weapons for self-defense—long guns, for example—was therefore not enough to save DC’s law.

What arguably emerges from Heller, then, are not two but three categories of arms. “Dangerous and unusual” weapons are categorically excluded from coverage and can be banned without raising any constitutional concerns. They are the equivalent of libel or securities fraud under the First Amendment. Weapons “in common use” are covered by the Second Amendment, so bans involving them are subject to scrutiny—a prohibition on high-powered rifles or high capacity magazines, for example, must be appropriately tailored to a sufficient government interest. Finally, within the general set of constitutionally covered common-use weapons, some classes cannot be banned, regardless of the efficacy of the law or the government interests involved. This last category includes handguns, which Heller emphasized have a unique connection to self-defense. Are there other classes of arms that are similarly immune from bans? (I try to unpack that and related questions in “Bans,” which is forthcoming soon in the Yale Law Journal and from which some of this discussion is drawn.)

Some judges seem to have concluded that any arm (or “hardware”) in common use is immune to prohibition. In Duncan v. Becerra—an unusual opinion involving California’s restriction on high capacity magazines, which, it’s safe to say, will not be the last word on the subject—the district court concluded that Heller provides a test that is “simple” and “crystal clear.” According to the judge in that case, “It is a hardware test. Is the firearm hardware commonly owned? Is the hardware commonly owned by law-abiding citizens? Is the hardware owned by those citizens for lawful purposes? If the answers are ‘yes,’ then the test is over.”

The test is simply stated, perhaps, but hardly “crystal clear” in practice, for reasons that Eugene Volokh and many others have pointed out ever since Heller. What counts as “common”? For that matter how does one separate one set of “hardware” from another? For purposes of evaluating constitutionality in a case involving high-capacity magazines, does one count all magazines over 10 rounds? 20?

The definitional problems are even harder when one tries to apply them to firearms. Handguns might seem like a natural category, and maybe it is. But if one tries to get much more specific than that, the divisions feel less like a taxonomic exercise and more like an effort to list cosmetic features. Indeed, one common line of argument against assault weapons bans is that they are an irrational effort to target scary-looking guns. But that definitional argument cuts both ways. If would-be regulators can’t define a class of arms with requisite precision, can gun rights advocates do any better?

Fundamentally, though, the problem has less to do with definitions than it does with constitutional principle. Under what plausible account of the right to keep and bear arms should a weapon’s commonality render it immune to prohibition? What Second Amendment value does that protect? Adopting a rule that is “crystal clear” but tracks no underlying constitutional principle means not just elevating form over substance, but actually ignoring the latter.

In their concurring opinion in Caetano, Justices Alito and Thomas wrote that “the right to bear other weapons is ‘no answer’ to a ban on the possession of protected arms,” citing Heller. But the cited passage from Heller (the one quoted above) says only “[i]t is no answer to say … that it is permissible to ban the possession of handguns so long as the possession of other firearms (i.e., long guns) is allowed.” And since Heller also emphasizes that “ the American people have considered the handgun to be the quintessential self-defense weapon,” the passage seems to be saying only that there is no adequate alternative to handguns, not that the Second Amendment forbids any consideration of adequate channels of self-defense.

If handguns are the quintessential self-defense weapon, then it seems clear that long guns—including semi-automatic rifles—cannot be. They might be important, and they might be constitutionally protected, but that doesn’t make them immune to prohibition. As the D.C. Circuit put it in Heller II:

We simply do not read Heller as foreclosing every ban on every possible sub-class of handguns or, for that matter, a ban on a sub-class of rifles. . . . [T]he Court in Heller held the District’s ban on all handguns would fail constitutional muster under any standard of scrutiny because the handgun is the “quintessential” self-defense weapon. The same cannot be said of semi-automatic rifles.

In short, the fact that the handgun ban in Heller went too far and was per se unconstitutional does not mean that all “class of arms” rules should be subject to the same treatment.

I suspect that per se rules will continue to gain support among some judges, especially those who see themselves as limiting judicial discretion and providing principled protection for gun rights. I have my doubts that invocation of “bans” will deliver on either of those values.