Not long after I heard that Joni Mitchell had performed a surprise set at the Newport Folk Festival last night, I got a call from a friend who loves Mitchell's music even more than I do. We were talking about our paths through life, and the way momentous decisions can come to seem inevitable, but only after you've made them. The friend brought up "Both Sides Now," perhaps Mitchell's first perfect song, which she first performed at 23, not long after giving up her baby daughter for adoption and moving to the U.S. The song widens its scope with each verse, looking first at clouds, then at love, and finally at life itself, taking in the light and dark of each. A poet, or a songwriter, is an observer of her own life as well as a participant, eyeing each situation as possible material even as she's experiencing it. The Joni Mitchell of "Both Sides Now" relishes observation but also recognizes its limits: she's looked at life from both sides, and admits she knows little about actually living.

My friend asked me: Do you think Joni still feels that way? It would be a comfort as well as a terror, knowing that our hero, at the twilight of her extraordinary life, remains so uncertain. I don't know the answer, of course, but I said to my friend, I think she probably does still feel that way sometimes. Just listen to the version of "Both Sides Now" she released in 2000, 30 years on from the original. The featherlight voice of her youth has deepened and darkened, and the crisp acoustic strumming of the original has become an orchestral arrangement that gathers and disperses like morning mist. The words are the same, but their implications are different. For all its attunement to melancholy, the recording on 1969's Clouds rides on an undercurrent of optimism, a sense that the true nature of things may eventually reveal itself to the singer. The 2000 version replaces that cheer with weary resolve. Time has passed, and the current is slowing. The answers are no nearer to sight.

I waited until this morning to watch footage from last night's performance, Mitchell's first full concert since 2000, because I (correctly) sensed that it would bring me to tears. For a fan who never got the chance to see her perform, and figured she wouldn't return to it after her 2015 brain aneurysm, even small details are almost too much to bear: the way she boogies along in her chair as the band plays "Carey"; the sudden smile that signals her mounting confidence as she works through a solo instrumental arrangement of "Just Like This Train"; the fact that she's still playing a Parker Fly, the frankly ridiculous-looking electric guitar she began favoring in the 1990s, and still making it look so cool. A chorus of friends and admirers surrounds her - Brandi Carlile, Blake Mills, Wynonna Judd, and others - strumming and singing along, picking up the occasional dropped lyric. But the best moments come when their voices fall away and Mitchell carries the tune on her own, her voice even deeper than it was in 2000.

The set is filled with lines that feel even truer now than they did from the mouth of a younger person: "People will tell you where they've gone/They'll tell you where to go/But 'til you get there yourself, you'll never really know," in "Amelia"; "We can't return, we can only look/Behind, from where we've came," in "The Circle Game." It's possible that someone calibrated the set list deliberately in this direction, choosing songs that would gain new power from the perspective of old age. It's also true that Mitchell could have plucked many other songs from her catalog that would have been equally appropriate to the occasion: tough and tender, hopeful but undeluded, sharing the complicated wisdom gained from a life spent in observation.

The glowing center of the performance is "Both Sides Now." She sings it as a duet with Carlile, who delivered several other songs in Mitchell's original vocal register, an octave higher than where she's singing now, an effect that gave a flickering illusion of the aged songwriter trading verses with her younger self. For "Both Sides Now," Carlile goes low too, and stays mostly in the margins, so that we only hear Mitchell as she sounds today. The arrangement is stately, much like the 2000 recording, allowing her to linger on lines that pass by quickly on the original. "Tears and fears and feeling proud/To say 'I love you' right out loud," she sings slowly, presenting that display of vulnerability in the face of uncertainty as a feat of strength. "But now old friends are acting strange/And they shake their heads and they tell me that I've changed," she continues, ascending through the melody with casual grace. "Well something's lost, but something's gained/In living every day." I found myself wondering, not whether this song still carries any resonance for Mitchell at 78, but how she managed to write it in her early twenties.