The latest and deadliest addition to America's grotesque gallery of mass shootings defies the classifications we try to impose on such crimes in a futile effort to make sense of them.

Omar Mateen, the killer of nearly 50 men and women whose fatal decision was to go out and dance on a Saturday night, declared allegiance to the extremist group Islamic State in the midst of the massacre in Orlando, rendering it an act of terrorism. Bigotry also apparently motivated him to target a gay club, making it a hate crime. And his ex-wife and others described him as isolated and unstable, suggesting parallels to similar crimes blamed on mental illness.

Of course, the perpetrator of such an unfathomable act can't be expected to have a clear and coherent rationale. But the confusion in this case underscores the impossibility of restraining such violence by addressing every potential motive. Efforts to combat Islamic State, check bigotry, and treat mental illness are as worthwhile as they are unlikely to prevent the next killer from finding a cause.

The FBI's monitoring and questioning of Mateen could not prevent the shooting in the absence of evidence of a prior crime. Neither did the presence in the nightclub of armed security. And neither did permissive Florida gun laws empowering every citizen to become the mythic "good guy with a gun" who could stop similarly enabled bad guys.

The common denominator of mass shootings, besides the pointlessly ended and damaged lives of victims and their loved ones, is the shooting. That's why the inescapably pertinent fact of firearms keeps coming up despite our hopelessly paralyzed political debate and inability to make a modicum of progress on the issue. If any progress can be made against such slaughter, it will be by limiting access to deadly weapons as well as the degree of their deadliness.

For all the awful diversity of victims, killers, and twisted ostensible motives, what has further united many of the decade's deadliest shootings - including the assaults on a California office party, an Oregon community college, a Connecticut elementary school, and a Colorado movie theater - has been the perpetrators' access to legal, high-powered, semiautomatic rifles. Designed to kill people quickly and efficiently, such formerly banned weapons make casualty counts like last weekend's far more probable.

Other mass shootings have used less powerful firearms but might have been prevented or mitigated by universal background checks of the kind Congress has tried but failed to enact. Meanwhile, the all too commonplace gun violence that plagues America's cities - about 2,000 gun crimes have been reported in Philadelphia over the past six months, more than five times the number of mass shootings nationwide last year - are more likely to be affected by laws designed to stem the illegal gun trade.

We can't prevent every act of gun violence with any amount of legislation. But we could certainly reduce the country's uniquely high toll of shooting deaths without infringing on the constitutional right to bear arms. The fact of the matter is that we have repeatedly chosen not to do so - and thereby repeatedly chose what happened in Orlando.