In his concurring opinion, Justice Samuel Alito first established that the Second Amendment protects an individual’s right to keep and bear arms, and that right is applicable against both the State and Federal governments. Alito then states that the Second Amendment right “vindicated the ‘basic right’ of ‘individual self-defense.’” Alito then observed that Caetano’s use of a stun gun “illustrates the connection” between the right to keep and bear arms and self-defense, and he commended her for “using a weapon that posed little, if any, danger of permanently harming either herself or the father of her children.”

Alito dismissed the Massachusetts court’s argument that Caetano could have just purchased a handgun to defend herself, writing that “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.” He added that “the right to bear other weapons is ‘no answer’ to a ban on the possession of protected arms.” On this point, Alito concluded that “[c]ourts should not be in the business of demanding that citizens use more force for self-defense than they are comfortable wielding.”

Evaluating the lower court’s “ill treatment” of Heller, Alito stated that it “cannot stand.” The lower court limited their analysis to whether a particular weapon was in common use at the time of the Second Amendment’s enactment, but Alito emphasized that the argument ‘that only those arms in existence in the 18th century are protected by the Second Amendment’ not merely wrong, but ‘bordering on the frivolous.’” Alito then reminded the lower court that Heller clearly held that “even those that were not in existence at the time of the founding” are within the scope of the Second Amendment’s protection. He added, “[i]t is hard to imagine language speaking more directly to the point.” Alito pointed out that the most popular weapons in modern America were not in existence at the time of the founding, so such a standard would be arbitrary. Alito emphasized the applicability of the Second Amendment to modern weapons, writing that “[e]lectronic stun guns are no more exempt from the Second Amendment’s protections, simply because they were unknown to the First Congress, than electronic communications are exempt from the First Amendment, or electronic imaging devices are exempt from the Fourth Amendment.”

Alito then stated that the relevant Second Amendment inquiry is whether stun guns are commonly possessed by law-abiding citizens for lawful purposes today. Alito dismissed the argument that the number of tasers and stun guns is far less than the number of firearms, writing that if such a standard were used, “a State would be free to ban all weapons except handguns, because ‘handguns are the most popular weapon chosen by Americans for self-defense in the home.’” Alito affirmed that the relevant statistic is that hundreds of thousands of tasers and stun guns are owned and used for self-defense by individuals across the country, and its use is legal in 45 states. Ultimately, Alito concluded that “Massachusetts’ categorical ban of such weapons therefore violates the Second Amendment.”