“The big thing about language is that it always changes,” David Crystal, the author of “Making a Point: The Persnickety Story of English Punctuation,” said. Photograph by Dave Bradley/Getty

“People don’t know why they get so upset about language,” David Crystal told me recently, over Skype from his home in Wales. “ ‘Potato’s,’ with an apostrophe ‘S,’ ” he offered, as an example of the kind of thing that drives some people batty, “but you ask them, ‘Why are you so upset?’, and they can’t answer you.” Crystal is an independent linguist and the author, co-author, or editor of more than a hundred books about language. His newest book, “Making a Point: The Persnickety Story of English Punctuation,” takes for granted that we all have anxiety—and, therefore, curiosity—about punctuation. His response to this anxiety is to explain calmly but firmly how punctuation rules came to be.

“There are two extreme views about punctuation,” he writes, “the first is that you dont actually need it because its perfectly possible to write down what you want to say without any punctuation marks or capital letters and people can still read it youdontevenneedspacesbetweenwordsreally.” The second view is that punctuation is essential, not only to avoid ambiguity but also because it “shows our identity as educated people.” Crystal walks the reader through the history of punctuation, from scriptura continua—that is, words written without spaces between them—to the more punctuated present. In Old English manuscripts, punctuation is idiosyncratic; to denote word divisions, writers tried a variety of strategies: dots, spaces, “camel case” (that is, using capital letters rather than spaces ToMarkTheBeginningsOfNewWords). Then the rise of printing created the demand for a standardized system.

After the historical overview, “Making the Point” shifts gears: it becomes equal parts practicum and commentary, usage manual and style guide. Crystal teaches readers the difference between an en dash and an em dash; gives the history of the serial comma (which the book, like The New Yorker, uses); and illustrates how hyphens in words such as to-day, bumble-bee, and ice-cream disappeared between the fifth (2002) and sixth (2007) editions of the Oxford English Dictionary. As for contemporary rules, he advocates “pragmatic tolerance.” Know them, he argues, so that you can break them, when they should be broken.

“The big thing about language is that it always changes,” Crystal told me. “Since the Internet came along, it has never moved so fast.” This has helped to make finger-wagging very popular. Lynne Truss’s 2004 best-seller “Eats, Shoots and Leaves,” for instance, cried that “everywhere one looks, there are signs of ignorance and indifference.” In 2008, Crystal published “Txtng: The Gr8 Db8,” a response to what he describes as the “moral panic” that had been spreading in the United Kingdom and the United States since around 2000, when texting became an everyday experience. A 2007 Daily Mail article titled “I h8 txt msgs” had declared that “SMS vandals” were “pillaging our punctuation; savaging our sentences; raping our vocabulary. And they must be stopped.” Crystal rebuffed these drastic claims: the supposed “innovations” of texting, he notes—abbreviations, omitted letters, ideograms, nonstandard spellings—have been features of the language for centuries.

Seven years later, that db8 seems quaint. Daniel Donoghue, who teaches a course on the history of English, at Harvard (I was a teaching fellow for the course last year), said that just after “Txting: The Gr8 Db8” was published, an undergrad told him that Crystal’s title was already outdated: phone technology has made alphabet texting so easy that “anyone going for the shortcut ‘gr8’ was proclaiming how behind the times she was.” (Louis Menand made a similar point when he wrote about the book for this magazine.) Crystal wrote to me that “very few older kids in the UK use txtese abbreviations now. They're not cool any more. One student told me recently that he stopped abbreviating when his parents started!”

The moral panic about the Internet’s effect on language also seems to have quieted. “I don't think anyone talks these days like the prophets of doom a couple of decades ago,” Crystal said. In a 2013 TED Talk, “Texting Is Killing Language. JK!!!”, the Columbia University linguist John McWhorter dismantled the myth that the Internet has eroded linguistic competence. Texting, McWhorter declared, is not a scourge but a “balancing act” and “an expansion of [people’s] linguistic repertoire.” In a 2015 epilogue to his 2007 book “Inventing English,” the historical linguist Seth Lerer also dismisses the notion that the Internet and new technologies herald the end of English as we know it. “This is, for now, our language,” Lerer writes, “and if we take liberties by writing on a screen or talking in face time rather than face-to-face, we are sustaining a tradition of a thousand years of re-inventing English.” As Crystal writes in “Making a Point,” “Standard English punctuation is still alive and well; in the online world, nonstandard punctuation is alive and well.… Quite a few online sites—most of the Web, and many bloggers and social networkers—remain faithful to traditional punctuation norms.”

Sociolinguists use the term “diglossia” to describe a society that employs two distinct versions of a language—Classical and colloquial Arabic, for instance—and Crystal sees the Internet as creating a similar phenomenon (though he calls it “digraphia,” since he’s dealing strictly with written language). Another analogy is code-switching, which happens when someone alternates between two or more varieties of spoken language in different conversations (and sometimes within a single conversation). Historical linguists see language usage on the Internet not so much as the downfall of Standard English but as another example of this kind of intuitive interplay. “Because of code-switching, I’m not so concerned that the Internet will destroy civilized communication as we know it,” Donoghue told me. “It certainly doesn’t have to become the angel of destruction if those of us charged with teaching how to use language, including parents, do our jobs.”

Crystal says he’s learned not to guess where the future will take language. “If you had predicted one thousand years ago that nobody would know Latin, people would have said you were mad.” And he’s not interested in creating a bible of best practices; rather, he wants to help people understand the tools they’re already using. That apostrophe that pops up sometimes in “potato’s” and in other plural nouns? People have taken to calling it the “greengrocer’s apostrophe,” because of its frequent appearance on signs for produce (“banana’s” is another common offender). It can be traced to a time before current apostrophe usage had been codified, when people often used apostrophes to signal in an obvious way that a word ending in a vowel was in fact a plural noun.

Does knowing that history make seeing the outdated usage today less irritating? Maybe, maybe not—but it is interesting. “Language is for everybody,” Crystal said. “Human beings, homo loquens, the speaking animal. I’ve never met anybody who isn’t profoundly interested in language.”