O.K., the new like is hot and it’s useful, but is it legit? Aren’t some rules of grammar or usage being broken here?

Linguists and lexicographers say no. It’s natural, they say, for words to take on new roles. In this case, a “content word” (one that means something) has become a “function word” (one that has a grammatical function but little actual meaning). Academics call the process “grammaticalization.” It’s one of the ways language changes.

So is the new like proper English? Well, the latest editions of The American Heritage Dictionary of the English Language and Merriam-Webster’s Collegiate Dictionary now include it as a usage heard in informal speech. That’s not a ringing endorsement, but it’s not a condemnation either.

As for me, I’m convinced that this is a useful, even ingenious, addition to informal spoken English. But let’s be honest. For now, at least, it smacks of incorrectness to a great many people. In writing my grammar book for kids, I wrestled with this problem. In the end, I suggested that the usage is O.K. in informal conversation but not for situations requiring your best English.

Contrary to popular opinion, like is not exclusively a kid thing. Grown-ups use it too, men and women about equally, according to Dailey-O’Cain.

“Part of what inspired my study was the fact that my mother (who was in her 50s at the time) used to complain about other people using like,” she says. “But once I started pointing it out to her every single time she used it herself, she stopped making those kinds of criticisms!”

The linguist Geoffrey Pullum, an author of The Cambridge Grammar of the English Language, finds the usage “quite logical and reasonable.” And he agrees that it’s not confined to youngsters. “My former student Jessica Maki caught her 65-year-old aunt, who grew up in North Carolina, saying, ‘I’m like, don’t answer the telephone!’ ”