With its landmark ruling in District of Columbia v. Heller, the Supreme Court has put to rest a fashionable bit of constitutional revisionism, that the Second Amendment protects the states’ power to arm militias, rather than the people’s right to keep and bear arms. That interpretation led to numerous laws restricting gun ownership, including the District of Columbia’s effective ban on keeping handguns in the home. Despite all that activity, however, the Supreme Court had never explicitly stated whose prerogatives the amendment protects.

The Supreme Court put an end to that reticence last week when it came down squarely on the side of the individual-rights interpretation. In so doing, the court struck down the D.C. gun ban as a clear violation of that right.

Yet the court also recognized that this right is not absolute. “Like most rights,” Justice Antonin Scalia wrote for the majority, “the right secured by the Second Amendment is not unlimited.” The court offered no opinion, however, on exactly where that right ends, and reasonable regulation begins.

For example, the court did not disturb D.C.‘s requirement that all gun owners be licensed. Federal, state, and local officials, as well as the American public, must now grapple with that question, which may ultimately end up back before the high court.

Our inquiry should start with the recognition that the right to keep and bear arms is a natural outgrowth of the right to self-defense. We possess an inherent right to keep and bear arms so that we may have the means necessary to defend ourselves against acts of violence.

Your neighbor has a right to keep a gun in his home to defend himself, because the threat of home invasion is real. But your neighbor does not have a right to keep a nuclear weapon in his home, because it is not reasonable to think that he would need such a weapon to defend himself.

The right to self-defense thus creates a bulwark that government regulation of arms may not breach. If a weapon would permit a proportionate defense against a reasonably foreseeable threat, the government cannot prohibit you from owning or carrying it.

That rule reconciles the right to self-defense with the right not to be tailgated by an armored tank in the passing lane. That wacko in your rear-view mirror does not have a right to own armored tanks or shoulder-mounted rocket launchers, because he does not need them to defend himself.

Many gun control laws would fall under this rule. If it is reasonable to expect that a person could be assaulted while walking down the street, then a ban on carrying handguns would violate an individual’s right to defend herself. If it is reasonable to expect that assailants pick victims who appear unarmed, then a ban on carrying concealed handguns would fall.

At the same, other gun control laws could survive. The current restrictions on fully automatic weapons could be upheld if no citizens face a reasonable threat against which they would need an Uzi to protect themselves. Requirements that guns be licensed or that sellers conduct background checks could also survive. Yet that should not be the only hurdle that such laws must clear.

Legislatures and courts should weigh the costs and benefits of regulations, including a restriction’s impact on gun-related violence or whether it poses a threat to the underlying rights at stake. If banning fully automatic weapons or 50-caliber rifles doesn’t reduce gun violence, then what’s the point?

Moreover, though it allows reasonable regulation of firearms (i.e., a “ceiling”), the right to self-defense does not by itself constitute the “floor” beneath the right to keep and bear arms. The court in Heller acknowledged Second Amendment protects other activities as well, including hunting and recreation, so long as they pose no particular threat to others. To be reasonable, regulation must respect those purposes of the right to keep and bear arms as well.

The Heller case closes one chapter in our national debate over our Second Amendment rights. The next chapter begins now.