When I go to a blues concert these days, what I hope for is something bold and strident, something defiant and electrifying in the style of Muddy Waters or Howlin’ Wolf. But if I had to choose one blues track to take to a desert island, it would be Blind Willie Johnson’s Dark Was the Night, Cold Was the Ground.

Ry Cooder called it “the most spiritual, transcendent piece in all of American music”, and used it as the basis for his haunting Paris, Texas soundtrack, which is where I must have heard it first, though I didn’t know it then.

There are no words to the song. There is only his slide guitar, accompanied by his gravelly moans. Because of the way he bends the notes it is uncertain whether the song is in a major or minor key, but the longing at its centre is unmistakable.

In 1977 Carl Sagan was looking for samples of music to include on a Golden Disc that was to be sent out into space on the Voyager space craft, the idea being to represent to whatever life forms were out there as much of human experience as was possible. Sagan and his team chose Dark Was the Night, Cold Was the Ground as an expression of human loneliness.

I like to think of Johnson’s dark music floating into space, defying gravity as it travels towards an unknowable destination. But there is something earthbound in the song, as its title suggests. One doesn’t have to refer to the meager biographical information we have about Johnson’s life. Listen to the slow way the notes bend: there is joy mixed in with the longing, but it takes a long time to reach them.

I have noticed the same tendency to slide into a note rather than hitting it directly in recordings of South African choral music. The effect is one of longing for something that is never specified, no matter how happy, even triumphant, the words may be.

A friend of mine, who had made many field recordings of such choral singing, had the good fortune to meet the great bluesman Taj Mahal in the US some years ago and expressed surprise at this similarity, as these rural South Africans would never have heard the blues. Taj Mahal answered that it isn’t necessary to hear the blues to understand them – you just need to have them.

In spite of the apparent resolution at the end of the song, a question hangs in the air each time it stops playing. Carl Sagan heard it, and associated it with the plight of all those who face the sunset without knowing where they will sleep that night. The closest we can come to Johnson’s own thoughts and feelings is through the body of his work. In one of his best-known songs he asks repeatedly: “Won’t somebody tell me, answer if you can / Want somebody tell me what is the soul of a man.” This is the territory Johnson explores, bending those notes with his guitar and voice as if he wants to pluck everything life has to offer out of them.