Joni Mitchell built her name on guitar tunings nobody else used and lyrics sharp enough to draw blood, and if that was all she'd done she'd still be one of the great songwriters of her era. But by the mid-1970s she was bored of the boxes people put her in, and she started writing songs that didn't resolve the way pop songs are supposed to — melodies that drift, chords that hang open, phrasing that talks instead of sings. That's when jazz musicians started showing up on her records, and it's why she belongs in a book like this one.

Hejira (1976) is the record to start with. It was written mostly while she was driving across the country alone, and it sounds like it — spacious, unhurried, full of long lines that don't want to end. The bass player is Jaco Pastorius, and what he does on that record is not really bass playing in the traditional sense. He floats under her voice, answers her guitar lines, sometimes just about takes over the song. It's one of the strangest and best pairings in 1970s music, a fretless bass virtuoso decorating a folk singer's tour diary.

Then came Mingus (1979), which is the boldest thing she ever did. Charles Mingus was dying, he'd lost the ability to play, and he asked Joni Mitchell — a folk singer, not a jazz musician — to write lyrics to some of his last melodies. She said yes, brought in players like Wayne Shorter, and made a record that is half tribute, half interview, half something else entirely. It confused a lot of her old fans. It's also one of the more honest things anyone tried to do with jazz in that decade.

The touring band she put together around that period reads like a fusion dream team — Pat Metheny, Michael Brecker, Lyle Mays, Wayne Shorter would keep turning up on her records for years after. She wasn't trying to become a jazz singer. She was trying to find musicians who could keep up with where her songs wanted to go, and it happened that those musicians were jazz players, because nobody else could follow her chord voicings without a map.

What you're left with is an artist who isn't really a jazz artist but who made a handful of records that jazz listeners keep coming back to, because the harmony is genuinely strange and the collaborators are genuinely serious. If you want to hear a songwriter push past what songwriting is supposed to sound like, start with Hejira, sit with Mingus, and don't expect it to behave.