Steven Pinker, author of “A Sense of Style,” says old style manuals are obsolete. (Rebecca Goldstein)

Steven Pinker’s new book, “The Sense of Style,” offers “The Thinking Person’s Guide to Writing in the 21st Century.” He spoke from Boston.

Why do we need a new style book?

The style manuals from the second half of the 20th century are literally obsolete, and we have to reflect the fact that language changes. In “The Elements of Style,” Strunk and White prohibit the verb “to contact” and the verb “to finalize.” In their day, that sounded like slang, jargon, pretentious business-speak. Today they’re indispensable. And we know so much more about language than we did in the 20th century. We have laboratory studies on what makes sentences hard to understand. And we have a body of scholarship that traces the history of these controversies. That allows writers to distinguish the bogus rules from the helpful ones.

You emphasize that knowledge of grammar is important.

There are many accomplished writers who probably could not identify a relative clause if they banged into it in the middle of the night. But it’s helpful in evaluating writing advice, just as in any specialized pastime. You can’t perfect the art of photography if you don’t know what an f-stop is. You have a hard time perfecting the art of writing if you don’t know what a subordinate clause is. But grammar is much closer to a science than a set of commandments from a ruler-wielding nun.

Given that the meanings of words evolve — people will often use “prevaricate” these days to mean being indecisive, for example — how does one deal withthis conundrum?

Look it up. I’m going to practice what I preach and look it up right now. The American Heritage Dictionary gives as the first definition “to speak or write evasively, to lie.” The second — and it immediately flags it as a usage problem — is “to behave in an indecisive manner, delay or procrastinate.” Then there’s a usage note: 78 percent of the usage panel — a panel of writers and commentators and broadcasters, etc. — disapprove of the “delay” sense. For some usage controversies, like “fortuitous” to mean “fortunately,” the usage panel is more evenly split. So by using a dictionary with usage notes, a writer can get the lie of the land and make a choice accordingly.

Once you know you’re correct, what should you do over dinner?

It’s a matter of tact and social judgment. If somebody has their fly open, or spinach in their teeth, you’re doing them a favor, however embarrassing it might be at the time. Other times, it will be experienced as one-upmanship — you don’t want to come across as a smarty-pants.

Which common grammatical error most drives you crazy?

I’m not, in general, a peever. I don’t walk around with sensitive nerve endings for mistakes. I’m far more annoyed by lack of clarity, by people who write generically instead of concretely. I just read this morning a paper by a postdoc at Harvard writing about people who experience negative outcomes. What the hell does that mean? Were they fined, were they hit upside the head? The reader has no idea what’s actually taking place.

Burns is head of creative writing at the University of Southampton in England.