“THAT’S pants!” says the exasperated Londoner, confusing Americans. Why would anyone swear by pants? Transatlantic types know the reason: in Britain, pants are undergarments, in America they are mere trousers. Or at least that’s what the New York-London jet-set believes. But in the north-west of England, “pants” are trousers, just as they are in America (and just as they were first elsewhere in England). “Pants” as underpants is the newcomer.

Jack Grieve, a linguist at Birmingham University, uses Twitter to study regional patterns in English. Those who think Twitter is only good for being rude about others are dead wrong. Millions of people use Twitter for ordinary chitchat and unfiltered thoughts. This may be no great contribution to world literature, but it is a gold mine for dialectologists.

That’s because people on social networks write much as they speak. Dialectologists otherwise have a tough job. To find dialect words or expressions, they track down old people in the countryside, sit with them and patiently question them about their childhood, hoping to draw out distinctive local words and expressions. But it is time-consuming, allowing dialect researchers to interact with only a small number of speakers. They are nagged by the thought that they may not have found truly representative ones, or that they are missing changes afoot.

Enter big data. People writing on Twitter or Facebook leave an electronic data trail that can be gathered and analysed almost instantly. And in those media they put what they would say in speech into text, in a new mode of communication that John McWhorter of Columbia University has come to describe as “fingered speech”.

Fingered speech is perfect for the dialectologist who wants lots of data but is short of time. If people “talk” on Twitter as they do in real life, all you need is access to lots of tweets. Not all tweets are public, and not all show the location of the tweeter, but there are enough that they offer billions of bits of usable data.

Mr Grieve can make postcode-by-postcode maps showing dialect features. “Trousers” shows up as a stark white on his maps in north-western England, meaning the word is hardly used there. In the south-east “Trousers” is deep red. “Pants”, meaning trousers, is a dusky light blue in London and the south-east, but a dark blue in north Wales and the north-west. (Oddly, people don’t seem to talk about underwear much on Twitter.)

The same goes for other shibboleths. “Sofa” is near-universal in England, and “couch” dominant in Scotland. Smaller words are naturally harder for dialectologists using traditional methods to find. But with Twitter data, researchers can easily find the rarer “settee” enough times to show that it is popular in south Wales and in bits of the north of England.

The results are culturally interesting, too. Mr Grieve’s maps for “gosh” in America show this “minced oath” to be popular not only in Mormon Utah, but in a contiguous region of the inland south, from Texas to Oklahoma, Arkansas, Missouri, Tennessee and Kentucky. But contrary to what one might expect, it hardly shows up in the deep-Dixie states of Mississippi, Alabama and Georgia.

Things get even more interesting when Mr Grieve stacks his maps—some 9,000 of them—on top of each other to find bigger patterns. And here the mystery of “gosh” is solved: the inland south is heavily white and religious. Many blacks still live in the lowland south, where their ancestors worked as slaves. And black Americans, on the whole, speak (and tweet) differently from white ones, a fact that shows up brightly in Mr Grieve’s work: the south-east is easily the most distinct region on his map. In other words, these are not just dialect regions, but cultural regions. The second most distinctive difference in his maps comes from the rural-urban divide. The coasts and big cities use “bagel” and “avocado”; in rural and inland bits “truck” and “boots” abound.

That’s a lot of work to confirm stereotypes, but it has the advantage of capturing quickly what pollsters and cultural geographers could only speculate over with census data. Billions of data points also make the work robust. And last, Twitter can capture changes that would take traditional researchers—whether geographers or dialectologists—so much time that they might miss quick-moving developments. Tomorrow’s researchers have a lot to look forward to.