Today, in Caetano v. Massachusetts, the Supreme Court vacated a decision by the Supreme Judicial Court of Massachusetts that had concluded that the Second Amendment right to keep and bear arms does not apply to stun guns.  The Court’s per curiam opinion scolded the Massachusetts court for its failure to apply the proper legal tests under D.C. v. Heller and McDonald v. Chicago, and quite rightly so. The court did not reach the ultimate question of whether stun guns constitute “arms” for Second Amendment purposes, however, instead vacating and remanding the state court opinion.

The Court’s per curiam opinion is brief and biting. Here it is:

The Court has held that “the Second Amendment extends, prima facie, to all instruments that constitute bearable arms, even those that were not in existence at the time of the founding,” District of Columbia v. Heller, 554 U. S. 570, 582 (2008), and that this “Second Amendment right is fully applicable to the States,” McDonald v. Chicago, 561 U. S. 742, 750 (2010). In this case, the Supreme Judicial Court of Massachusetts upheld a Massachusetts law prohibiting the possession of stun guns after examining “whether a stun gun is the type of weapon contemplated by Congress in 1789 as being protected by the Second Amendment.” 470 Mass. 774, 777, 26 N. E. 3d 688, 691 (2015).

The court offered three explanations to support its holding that the Second Amendment does not extend to stun guns. First, the court explained that stun guns are not protected because they “were not in common use at the time of the Second Amendment’s enactment.” Id., at 781, 26 N. E. 3d, at 693. This is inconsistent with Heller’s clear statement that the Second Amendment “extends . . . to . . . arms . . . that were not in existence at the time of the founding.” 554 U. S., at 582.

The court next asked whether stun guns are “dangerous per se at common law and unusual,” 470 Mass., at 781, 26 N. E. 3d, at 694, in an attempt to apply one “important limitation on the right to keep and carry arms,” Heller, 554 U. S., at 627; see ibid. (referring to “the historical tradition of prohibiting the carrying of ‘dangerous and unusual weapons’”). In so doing, the court concluded that stun guns are “unusual” because they are “a thoroughly modern invention.” 470 Mass., at 781, 26 N. E. 3d, at 693–694. By equating “unusual” with “in common use at the time of the Second Amendment’s enactment,” the court’s second explanation is the same as the first; it is inconsistent with Heller for the same reason.

Finally, the court used “a contemporary lens” and found “nothing in the record to suggest that [stun guns] are readily adaptable to use in the military.” 470 Mass., at 781, 26 N. E. 3d, at 694. But Heller rejected the proposition “that only those weapons useful in warfare are protected.” 554 U. S., at 624–625.

For these three reasons, the explanation the Massachusetts court offered for upholding the law contradicts this Court’s precedent. Consequently, the petition for a writ of certiorari and the motion for leave to proceed in forma pauperis are granted. The judgment of the Supreme Judicial Court of Massachusetts is vacated, and the case is remanded for further proceedings not inconsistent with this opinion.

Justice Samuel Alito, joined by Justice Clarence Thomas, wrote a separate opinion concurring in the judgment. He was even more critical of the decision below and would clearly have preferred for the court to have addressed the ultimate issue. Here’s a taste of Alito’s opinion:

It is settled that the Second Amendment protects an individual right to keep and bear arms that applies against both the Federal Government and the States. District of Columbia v. Heller, 554 U. S. 570 (2008); McDonald v. Chicago, 561 U. S. 742 (2010). That right vindicates the “basic right” of “individual self-defense.” Id., at 767; see Heller, supra, at 599, 628. Caetano’s encounter with her violent ex-boyfriend illustrates the connection between those fundamental rights: By arming herself, Caetano was able to protect against a physical threat that restraining orders had proved useless to prevent. And, commendably, she did so by using a weapon that posed little, if any, danger of permanently harming either herself or the father of her children.

Under Massachusetts law, however, Caetano’s mere possession of the stun gun that may have saved her life made her a criminal. See Mass. Gen. Laws, ch. 140, §131J (2014). When police later discovered the weapon, she was arrested, tried, and convicted. The Massachusetts Supreme Judicial Court affirmed the conviction, holding that a stun gun “is not the type of weapon that is eligible for Second Amendment protection” because it was “not in common use at the time of [the Second Amendment’s] enactment.” 470 Mass., at 781, 26 N. E. 3d, at 693.

This reasoning defies our decision in Heller, which rejected as “bordering on the frivolous” the argument “that only those arms in existence in the 18th century are protected by the Second Amendment.” 554 U. S., at 582. The decision below also does a grave disservice to vulnerable individuals like Caetano who must defend themselves because the State will not. . . . .

The lower court’s ill treatment of Heller cannot stand. The reasoning of the Massachusetts court poses a grave threat to the fundamental right of self-defense. The Supreme Judicial Court suggested that Caetano could have simply gotten a firearm to defend herself. 470 Mass., at 783, 26 N. E. 3d, at 695. But the right to bear other weapons is “no answer” to a ban on the possession of protected arms. Heller, 554 U. S., at 629. Moreover, a weapon is an effective means of self-defense only if one is prepared to use it, and it is presumptuous to tell Caetano she should have been ready to shoot the father of her two young children if she wanted to protect herself. Courts should not be in the business of demanding that citizens use more force for self-defense than they are comfortable wielding.

Countless people may have reservations about using deadly force, whether for moral, religious, or emotional reasons—or simply out of fear of killing the wrong person. . . . “Self-defense,” however, “is a basic right.” McDonald, 561 U. S., at 767. I am not prepared to say that a State may force an individual to choose between exercising that right and following her conscience, at least where both can be accommodated by a weapon already in widespread use across the Nation.

* * *

A State’s most basic responsibility is to keep its people safe. The Commonwealth of Massachusetts was either unable or unwilling to do what was necessary to protect Jaime Caetano, so she was forced to protect herself. To make matters worse, the Commonwealth chose to deploy its prosecutorial resources to prosecute and convict her of a criminal offense for arming herself with a nonlethal weapon that may well have saved her life. The Supreme Judicial Court then affirmed her conviction on the flimsiest of grounds. This Court’s grudging per curiam now sends the case back to that same court. And the consequences for Caetano may prove more tragic still, as her conviction likely bars her from ever bearing arms for self defense. . . . If the fundamental right of self-defense does not protect Caetano, then the safety of all Americans is left to the mercy of state authorities who may be more concerned about disarming the people than about keeping them safe.