When Joni Mitchell recorded "A Case of You" for her 1971 masterpiece Blue, the track included guitar backing from James Taylor, her boyfriend at the time. But onstage in London on April 22nd, 1974, Mitchell performed it alone, befitting the song's lyrics: It's a song about the first blush of love, but regarded after infatuation has passed and romance has crumbled.

Accompanying herself on dulcimer, Mitchell never sounded sweeter, or lonelier. The song begins, "Just before our love got lost, you said, 'I am as constant as a northern star,' and I said/'Constantly in the darkness - where's that at? If you want me I'll be in the bar.'" Her man didn't provide solace; nor did Shakespeare, the author of the "northern star" line (in Julius Caesar); nor did the bar. All that Mitchell had was the music, and so she leaned forward and gripped the dulcimer a little tighter.

The song's famous line "I could drink a case of you, darling/Still I'd be on my feet" may sound like a testament of devotion, but when you realize that it's about a relationship considered in the past tense, it has a different weight. Mitchell's also declaring that for all the passion in the relationship, it couldn't knock out her own equilibrium.

"One of my main interests in life is human relationships and human interactions," Mitchell told interviewer Malka Marom. "I really believe that individuality, the maintenance of individuality, is so necessary to what we would call a true or lasting love, that people who say 'I love you' and then begin to do a Pygmalion number on you are wrong, you know. Love has to encompass all the things that a person is."

One of the great rock & roll guessing games is to figure out the man who "A Case of You" was written about: Graham Nash is usually cited as the most likely suspect, but some advocate for others, such as Taylor or Leonard Cohen. But the gossipy aspect of the song pales next to the art that resulted and lyrics such as "I'm frightened by the devil/And I'm drawn to those ones that ain't afraid."

"The Blue album, there's hardly a dishonest note in the vocals," Mitchell told Cameron Crowe for a 1979 Rolling Stone interview."At that period of my life, I had no personal defenses. I felt like a cellophane wrapper on a pack of cigarettes. I felt like I had absolutely no secrets from the world and I couldn't pretend in my life to be strong. Or to be happy. But the advantage of it in the music was that there were no defenses there either."

By the end of this performance, Mitchell was keeping her eyes closed. Her heart remained open.