One afternoon in 2006, a novelist and a lawyer sat down with a camera and filmed an interview about the serious stakes of using words well. The two men, David Foster Wallace and Bryan A Garner, had cobbled together an awkward, touching friendship after Wallace published a laudatory review of Garner’s reference book. Despite postcards, letters and phone calls, they always seemed to just miss each other – a promise to meet the wife unfulfilled, a seminar scheduled one day off – so for years they’d go out of their way to grab dinner and shoot the linguistic breeze.

Garner, struggling with divorce, found Wallace to be “good counsel” for his troubles. Wallace could not overcome his own far more desperate troubles, though, and after struggling with depression his whole life, killed himself in 2008. With that interview and the story of their odd friendship, Garner has compiled a moving tribute to Wallace in Quack This Way.

The bulk of this slim volume (only 123 pages including the introduction) is the interview’s transcript, which reads like two old, very smart friends chatting about their favorite topic: how to write well. To adapt a relevant Guardian review, this introductory guide to writing "more than justifies the entry price". You couldn’t ask for two better tutors.

Wallace and Garner hash out the "lifelong apprenticeship" of language, from big bromides, like "the reader cannot read your mind", to the gritty details of good openers, transitions, and a vocabulary of "elegant variation". Their delight in taking apart solecisms is infectious – the passages about advertising and “officialese” are both hilarious and fascinating. It’s not as stunning as Wallace's essay – never mind as comprehensive as Garner's dictionary – but it’s still brilliant fun.

The friends' love for language is irrepressible. Garner's most staid questions turn into happy, roundabout digressions. He asks, for instance: "Of what utility is a usage book to some writer – of fiction or nonfiction?" In turn, Wallace talks about his students, a hard drive metaphor, and why a usage book "is one of the great bathroom books of all time".

DFW: Because it has the appeal of trivia, the entries are for the most part brief, and you end up within 48 hours … actually drawing on what you learned in some weird, coincidental way. So the bathroom usage-dictionary plug is now on film. BAG: Actually, my experience was the same; and I have frequently said that, but I always have to … DFW: Bathroom? The bathroom? BAG: Yeah! DFW: Outstanding!

The lessons on good writing are just one layer of the book; another is a record of friendship. These are two word nerds in their element, and you can hear each man’s personality ricochet off the other’s. Garner plays the encouraging square to Wallace’s self-deprecating novelist, who is in prime form. On drafts: "My first draft usually approximates somebody in the midst of an epileptic seizure." On good writing: “It’s like eating candy for the soul". On the ambiguous phrase “Beverages only in main cabin”: “Those poor thirsty first-class passengers”. On gesticulating at the camera:

DFW: This is okay? BAG: Yeah. I love this. DFW: You're very polite; I have no idea whether to believe you. We'll soldier on.

For each self-conscious deflection he has a slew of insights, about both language and people. Words reveal, disguise and manipulate people; people use words to communicate, connect and change each other. Awestruck, Wallace notes that the possibilities are limitless. So seems the conversation. The friends’ attention drifts – favorite novels, buried verbs, George W Bush – at one point landing on mid-life crises:

DFW: We go through cycles. Right? At least in terms of my own work, I've gone through three or four of these … it feels as if I've forgotten everything I've ever known. I have no idea what to do. And except on the days I'm really depressed, I realize that I've been through these before. These are actually good – one's being larval. … Who's the 45-year-old who doesn't know what she likes or what she wants to do? Is she immature? Or is she somebody who's getting reborn over and over and over again? In a way, that's rather cool. BAG: Could be that. Could be. DFW: But yeah, we both know immature schmucks. It's also a really great way to create drama in your life, right?

For all Wallace’s astute comments about human nature, Garner’s reflections are the ones that move you; by bridging the transcript to his introduction, he’s keeping Wallace alive for readers. Five years after the flood of grief that followed Wallace’s death – magazine essays, a biography, posthumous works – Garner has quietly published Wallace’s unedited voice, with royalties going to the university that holds the novelist’s archives.

Of everything Garner notes in his introduction – Wallace’s "ocapmycap@" email, tobacco tics, dinner with Antonin Scalia – its his own regret that’s most poignant. Knowing the feeling’s futile, he still writes: “I might have insisted that he keep me apprised of his narrative.”

And that is the book’s insistent message, about writing and life: pay attention. During the interview, Wallace reiterates this command over and over: slow down, reread, and attend to everything you’ve written, because each detail matters. Garner's grief strikes the same chord: step back, look around, listen to the people you care about, because they all matter. Garner hasn’t lost perspective either. When he’s unhappy, he rereads Wallace.

"It makes me happier – happier to know that there was such a man, such a mind, such a friend. His words uplift me. They give me hope. I'm not alone. Strange, isn't it, that he didn't find the hope within himself – the hope he gave to so many others."

Garner, with Wallace, set the stakes. The “lifelong apprenticeship” of writing well is the same apprenticeship of living well. This delightful, bittersweet book is a guide to the usage basics, a tribute to friendship, and an argument for paying attention to every word and person we can.