ON JUNE 12th Omar Mateen killed 49 people and injured 53 with a 9mm handgun and a semi-automatic gun called the Sig Sauer MCX, an AR-15-style rifle trumpeted by its manufacturer as “the first true mission-adaptable weapon system” which “eclipses everything that came before it”. Despite having been under FBI investigation in 2013 and 2014, Mr Mateen faced no obstacles when buying these weapons in the days before he walked into Pulse, a gay nightclub, in Orlando, Florida, and sprayed revellers with bullets. Many commentators are wondering anew why such a dangerous weapon is freely available for civilian purchase. The AR-15 has been the gun of choice in several other recent mass shootings, including the killing of 14 people attending a holiday party last December in San Bernardino, California; the murder of 12 in a movie theatre in Aurora, Colorado in 2012; and, later that year, the slaughter of 26 children and staff members at an elementary school in Newtown, Connecticut. The National Rifle Association (NRA) muses that the “AR” could stand for “America’s rifle”, as the AR-15 is the nation’s most popular long gun, with as many as 10m units in circulation. People gravitate to the AR-15 for hunting, sport shooting and self-defence, the NRA says, because “it is customisable, adaptable, reliable and accurate” as well as lightweight and easy to modify. Whereas its fully-automatic military cousin, the M16, shares its looks, the AR-15 shoots only one round per trigger-pull. It is thus a misnomer, gun-rights advocates say, to call the AR-15 a military-style “assault rifle”, a term that has been in use since Nazi Germany introduced the Sturmgewehr in 1944 (which in turn inspired the Soviet AK-47). Unlike fully automatic rifles, which can fire 750 to 900 rounds per minute and are available only to the armed forces, the AR-15 and its kin (sold by the millions to the general public) can muster only about 45 to 60. But as the Orlando tragedy showed, this circumscribed capacity can still be highly lethal.

Gun-control advocates began using the term “assault weapons” to refer to semi-automatic firearms like the AR-15 in the 1980s. In the wake of a school shooting in Stockton, California, the first President Bush approved a measure to prohibit importing such guns in 1989. In 1994, Bill Clinton signed the Federal Assault Weapons Ban, a law restricting the manufacture of large-capacity magazines and a large range of semi-automatic firearms. But due to a ten-year sunset provision, the ban was lifted in 2004 and efforts to reinstate it—along with attempts to pass other gun-control measures—have failed. Gun-rights advocates complain that the “assault” moniker is meaningless. It is used by gun-shy activists, a National Review article says, as “a sharp and effective tool with which the enemies of the right to keep and bear arms have sought to sow confusion, fear and ignorance”. The guns falling under the “assault” umbrella are “a set of quotidian weapons that have never posed much of a problem to anybody”.

After another mass shooting in which an AR-15 most certainly posed a problem to many people trapped inside a nightclub, such a blasé approach to powerful civilian weapons may be harder to maintain. Ludwig Wittgenstein, a great 20th-century philosopher and a veteran of the first world war, wrote in his “Philosophical Investigations” that when “we employ the word ‘meaning’,’’ we are most often referring to the everyday purpose of some phrase. “The meaning of a word”, he wrote, “is its use in the language”. By that sensible if trivial standard: if an AR-15 can be used to assault large crowds of people, killing and maiming scores of them, on multiple occasions, it qualifies as an assault weapon.