JUST weeks after the deadliest mass shooting in American history, in Las Vegas, America faced its fifth-worst attack, in Sutherland Springs, Texas, on November 5th. Both assailants were armed with military-style rifles. Why does American law let people buy such weapons?

The answer is the Second Amendment to the constitution, which reads: “A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.” (Commas were used differently in the 18th century, but these do not affect meaning.) Gun-rights advocates insist the second half of that sentence is absolute.

Those in favour of tighter regulation insist that the framers used the first clause to tie gun-rights to the need for a militia. Since no American state has the sort of militia that existed in the 1780s (consisting of all able-bodied men, subject to call-up at any time and expected to bring their own weapons), this would make wider curbs on guns legal.

What is that clause doing there? In the 1960s Paul Grice, a philosopher, wrote his seminal works on the unspoken rules of language, how often people observe them, and what they do when they break them. He codified these into several maxims of conversation now famous among linguists. One is the “maxim of relevance”: if someone randomly veers off-topic they break that maxim. The other is the “maxim of quantity”: speakers should say enough, but not too much.

These maxims can be broken. But because the maxims are so widely understood and observed, Grice argued, breaking them is significant. When you hear a speaker break them, your first instinct is to look for new meaning. For example, imagine a man arriving home, and his wife asking: “Where were you?” If he replies: “I am not cheating on you,” she would be right to be worried. Perhaps the information was supposed to be reassuring. But by breaking the maxim of relevance it sends an entirely different message.

Or take the maxim of quantity. Information should only be included for a reason. So what is the militia clause there for? Antonin Scalia tried to explain it in the Supreme Court’s opinion in DC v Heller, which in 2008 upheld an individual right to own and carry guns for hunting, self-defence or, really, for any reason. Like Grice, Scalia thought that the clause should be relevant. In fact, he insisted that it was. England’s Stuart kings had disarmed those likely to be disloyal. So an arms-keeping citizenry ready to muster as a militia, even against its own rulers, was indeed “necessary for the security of a free state”. Scalia said that prefatory clauses can announce a law’s purpose—but cannot restrict it.

Why have them, then? The writers of the constitution could have included all manner of philosophical navel-gazing in the prefatory clause: “The right of self-defence being inalienable…” and so forth. Some state constitutions did mention self-defence in their gun-rights clauses. The federal constitution does not. This makes the prefatory clause a rather odd bit of throat-clearing. If the framers meant to include self-defence, it violates the maxim of quantity by saying both too little (it did not mention self-defence) and too much (by not being needed at all).

A linguist at San Diego State University, Jeffrey Kaplan, argues that the prefatory clause is false. America, despite having no more militias, remains “a free state”, as do many other countries. He says that in parallel constructions like “Today being St Patrick’s Day, I will buy drinks for everyone in the bar,” if it turns out today is not in fact St Patrick’s Day, the promise in the main clause needs “repair”: a chance to cancel the offer or negotiate something else with the patrons. He put the St Patrick’s Day problem to 50 experimental subjects—80% said that if the presupposition was false, the offer was no longer operative.

In a second experiment, he invented a statute: “Water being an abundant resource, property owners shall have an unrestricted right to irrigate their property as they see fit.” If, a century later, water is now scarce, is the law still in effect? Of those who replied, 81% said no.

It is hard to believe the framers would be happy with the result of their work. America remains bitterly divided over guns, thanks to a bizarrely worded amendment that is introduced by a statement about militias that is superfluous (if Scalia and gun advocates are right), and was arguably never true at all. At the very least, it has not stood the test of time.