Why would anyone want a firearm?

A five-foot-tall, 110-pound woman is in a certain sense “armed” if she has a kitchen knife or a baseball bat at her disposal. But if the six-foot-four, 250-pound man who has broken into her apartment has one, too, she is not likely to overwhelm him. If that same woman has a nine-millimeter Glock, however? Well, then there is a good chance of her walking out unharmed. From the perspective of our petite woman, there is really no way for the state to endorse her right to defend herself if it deprives her of the tools she needs for the job.

In the sixth century, the Byzantine emperor Justinian compiled the monumental Digest of Roman Law, cataloguing the laws that had developed over centuries of Roman jurisprudence — among which was this rule of thumb: “That which someone does for the safety of his body, let it be regarded as having been done legally.” When it comes to the police and the armed forces, this principle is widely acknowledged, which is why most nations are happy to let their cops walk around with semi-automatic handguns and an array of advanced tactical gear. Within the civilian context, however, the same idea has become strangely controversial. Think of how often you hear Second Amendment advocates being asked with irritation why they “need” a particular firearm. Think, too, of how infrequently gun controllers focus on keeping weapons out of the hands of ne’er-do-wells rather than on limiting the efficacy of those available to the good guys. This makes no sense whatsoever. If a 15-round magazine and a one-shot-per-trigger-pull sidearm are necessary to give a trained police officer a fighting chance against a man who wishes him harm, there is no good reason that my sister shouldn’t have them, too.

As it happens, exactly this parity is presumed by America’s founding documents. The Declaration of Independence establishes that all men are born in possession of certain unchallengeable rights, and that among them are “life, liberty, and the pursuit of happiness.” This phrase, as with so many promulgated during the revolutionary era, is lightly adapted from John Locke, the English Enlightenment intellectual on whose philosophical presumptions the United States was in large part built. Inter alia, Locke held that every individual has a right to control and to defend his body, and that any government that attempted to deny that right was by necessity unjust. “Self defense,” Locke wrote in his Two Treatises of Government, “is a part of the law of nature” and in consequence cannot be “denied the community, even against the king himself.” In Locke’s view, this principle could be applied both on an individual level — against, say, intruders and other attackers — and on a collective level, against governments that turn tyrannical. Crucially, unlike Rousseau, Locke and his ideological heirs did not consider the establishment of the state to be a justification for the restriction of this principle.