Joni Mitchell was nine years old when she was sent to a polio clinic. She contracted the disease during an epidemic and was hospitalized for several weeks, during which she was told she would never walk again.

While in the clinic she would have been scared and bored and had ample time to read the children's seven book series, The Chronicles of Narnia by C.S. Lewis (who was member of the Inklings along with JRR Tolkein). The Dawntreader is the fifth book of the Narnia series.

The story of the of the Dawntreader is about a brother and sister sent away from their home to live with relatives who saw them as a burden, and an odious cousin who delighted in torturing them. All three children are drawn into the Narnia World through a picture of a ship at sea hanging on the wall of their attic bedroom. They are deposited on the ship called the Dawntreader. The children sail from island to island in the marine kingdom of Narnia, learning about the outcomes of evils such as slavery and greed. They also learn about the virtues of trust and kindness. They earn to be problem solvers, to think creatively and to be accepting of beings very different from themselves,

I believe that Joni saw the journey of the Dawntreader as a metaphor for her own bitter and sweet life experiences. Reading the lyrics, it seems clear:

And he learns to give
He aches and he learns to live
He stakes all his silver
On a promise to be free
Mermaids live in colonies
All his seadreams come to me

People talk about the song having a meaning. She is singing of the time she spent in the world we experience in dream... waking or sleeping. It's the world that lives alongside and with our 'waking' experience.

The meaning is the story of that journey.

She's been there. She's describing her journey there.

Our art , all of us, we do to describe this familiar and old place.

I recently rediscovered this song after many years. I was walking home from a private concert where the singer had done a cover of Blue. For some reason I looked for Sisotowbel Lane to listen to along the way but landed on The Dawntreader instead. The sublime trancelike vocals, the exquisite lyrics, and the haunting diatesserons of the accompaniment hit me straight in the plexus and I burst out crying right there in the street. I've read that Joni attributes her phenomenal artistic blooming in the late sixties to a kind of sublimation of yearning for her forsaken child. No other song represents that blooming quite like this one imho.

this is such a stoner song. if you've ever sailed a lot on a 32 footer on the great lakes or ocean with a beer or joint in hand, this is a song/album to play... along with carly simons album 'have u seen me lately' the song 'life is eternal' and the sun on the waves baby.