Even the most fanatical pedant must admit that usage is the ultimate arbiter of linguistic propriety. That is to say, a word means a certain thing because significant numbers of people take it to mean a certain thing. An informal process has evolved to monitor any shift in definition. At one end of the spectrum we meet words that will, from time to time, be “mistakenly” used in a way that does not conform to the dictionary definition. A chap might write “limpid” when he means “flaccid”. This still counts as an error. At the other end, we encounter words that, after decades of squabbling, have had their meaning formally transformed. Classical scholars will tell you that, derived from a term used by the Roman military, “decimate” used to mean the killing of one in 10 of any accused group. Now, we take it to mean the same as “annihilate” (which itself used to mean “make null and void”). The really interesting, contentious words can be found in the middle section of the spectrum.

A team of researchers walked every street in 228 census tracts around Los Angeles and New Orleans and recorded every outdoor ad they saw. Another group surveyed 2,881 residents of the same census tracts by telephone, paying them to report their height, weight and other information. After analyzing this hard-won data, the authors conclude: “For every 10 percent increase in food advertisements, the odds of being obese increased by 5 percent.” That is, areas with more outdoor food ads have a higher proportion of obese people than ones with fewer ads.

The problem is that their policy recommendations rest on a crucial but unjustified assumption: that any link between obesity and advertising occurs because more advertising causes higher rates of obesity. But the study at hand showed only an association: people living in areas with more food ads were more likely to be obese than people living in areas with fewer food ads. To be fair, the researchers correctly note that additional steps would be needed to prove that food ads cause obesity. But until those steps are taken, talk of restricting ads is premature. In fact, it is easy to imagine how the causation could run the opposite way (something the article did not mention): If food vendors believe obese people are more likely than non-obese people to buy their products, they will place more ads in areas where obese people already live. Suppose we counted ads for fitness-oriented products like bicycles and bottled water, and found more of those ads in places with less obesity. Would it then be wise anti-obesity policy to subsidize such ads? Or would the smarter conclusion be that the fitness companies suspect that the obese are less likely than the fit to buy their products?

When we seek to base policy on evidence, we must remember that not all “evidence” is created equal. Taken at face value, the study on ads and obesity provides some indication that the two are linked, but no evidence that food ads cause obesity. The fact that the causal conclusion may coincide with a moral belief — that it is wrong to tempt people who overeat by showing them ads for food — does not make it valid.

In the civil group, those who initially did or did not support the technology — whom we identified with preliminary survey questions — continued to feel the same way after reading the comments. Those exposed to rude comments, however, ended up with a much more polarized understanding of the risks connected with the technology. Simply including an ad hominem attack in a reader comment was enough to make study participants think the downside of the reported technology was greater than they’d previously thought. While it’s hard to quantify the distortional effects of such online nastiness, it’s bound to be quite substantial, particularly — and perhaps ironically — in the area of science news.

Languages are something of a mess. They evolve over centuries through an unplanned, democratic process that leaves them teeming with irregularities, quirks, and words like “knight.” No one who set out to design a form of communication would ever end up with anything like English, Mandarin, or any of the more than six thousand languages spoken today.“Natural languages are adequate, but that doesn’t mean they’re optimal,” John Quijada, a fifty-four-year-old former employee of the California State Department of Motor Vehicles, told me. In 2004, he published a monograph on the Internet that was titled “Ithkuil: A Philosophical Design for a Hypothetical Language.” Written like a linguistics textbook, the fourteen-page Web site ran to almost a hundred and sixty thousand words. It documented the grammar, syntax, and lexicon of a language that Quijada had spent three decades inventing in his spare time. Ithkuil had never been spoken by anyone other than Quijada, and he assumed that it never would be.

Recent factory fires in Pakistan and Bangladesh have killed more than 400 people. Yet, the stricken garment manufacturers had apparently passed inspection — despite bars on windows and locked exits — and been deemed safe. These factories supply clothing to — and are in business because of — American companies like Wal-Mart and Sears. So where does the responsibility lie in improving worker safety, and what can be done about it?

When water started trickling down a statue of Jesus Christ at a Catholic church in Mumbai earlier this year, locals were quick to declare a miracle. Some began collecting the holy water and the Church of Our Lady of Velankanni began to promote it as a site of pilgrimage.So when Sanal Edamaruku arrived and established that this was not holy water so much as holey plumbing, the backlash was severe. The renowned rationalist was accused of blasphemy, charged with offences that carry a three-year prison sentence and eventually, after receiving death threats, had to seek exile in Finland.

As the Technology Review reported:A significant proportion of the websites that this social media [around the Arab Spring] points to has disappeared. And the same pattern occurs for other culturally significant events, such as the the H1N1 virus outbreak, Michael Jackson’s death and the Syrian uprising. In other words, our history, as recorded by social media, is slowly leaking away.

So it seems that social media sites like Twitter do not remain as fecund a resource over time as they do in real time. But no historian has ever worked on the assumption that all, or even most, information about an event is preserved, let alone even recorded. Not even Twitter has changed that.

Nowadays, we’re very good at telling history in real time. Live-tweeting, livestreaming, Instagraming, link sharing, instant commenting — everyday lives and major events are recorded and narrated from every angle as they happen. A new study has found, however, that these minutes-old histories may not be built to last.