Arguably Joni Mitchell’s best song, “A Case of You” is about her breakup with Graham Nash (of Crosby, Stills, and Nash). In fact much of the album, Blue, captures the vulnerability and ache of that breakup.

She took some time off to travel, and wrote a lot of Blue from the island of Formentera, off Spain. In a 1979 Rolling Stone interview, she said, “At that period in my life, I had no personal defenses. I felt like I had absolutely no secrets from the world and I couldn’t pretend in my life to be strong. But the advantage of it in the music was that there were no defenses there either.”

On the surface, it’s a swooning love song, but it’s really about the complicated emotions of a deteriorating relationship: she’s calling out a man who promised her stability he is not delivering. “You said, I am constant as a northern star. And I said, constantly in the darkness.”

The song has been covered by over 200 artists, including the man who was its muse, Graham Nash, and acts as diverse as Sloan and Diana Krall.

James Taylor plays the acoustic guitar on the recording, and Joni the Appalachian dulcimer. She and Taylor had developed an intense, brief relationship that year, and the song “All I Want” is said to reference the relationship, right down to a sweater that she knit for him.

In 2011, Mitchell was voted the #1 female artist and “A Case of You” the #1 song by a female, by listeners of BBC Radio 4’s Desert Island Discs.