He goes on to share his ruminations on love, grief and change.
“I feel the presence of my son, all around, but he may not be there. I hear him talk to me, parent me, guide me, though he may not be there,” he wrote.
The 15-year-old fell from a cliff in Ovingdean Gap in the English seaside town of Brighton in 2015.
In his letter, Cave explained that Arthur visits Susie in her sleep, speaks to her and comforts her.
He described grief as a non-negotiable, terrible reminder of the depths of love.
“It seems to me, that if we love, we grieve. That’s the deal. That’s the pact.
“Dread grief trails bright phantoms in its wake. These spirits are ideas, essentially. They are our stunned imaginations reawakening after the calamity.”
He says that like ideas, “spirits speak of possibility”, as well as change, growth and redemption.
He explains that spirits are created by our imaginations, and implores his fan Cynthia to create and will those spirits alive to help lead her out of darkness.
“We are tiny, trembling clusters of atoms subsumed within grief’s awesome presence,” he wrote.
“It occupies the core of our being and extends through our fingers to the limits of the universe. Within that whirling gyre all manner of madnesses exist; ghosts and spirits and dream visitations, and everything else that we, in our anguish, will into existence.
“These are precious gifts that are as valid and as real as we need them to be. They are the spirit guides that lead us out of the darkness.”
In September, Cave suffered another loss when his bandmate 58-year-old pianist and keyboardist Conway Savage died from a brain tumour.
His 2016 album Skeleton Tree was touched by the effects his son’s death had on him, as did the documentary film One More Time with Feeling, which documented the recording of the sixteenth studio album.
Nicole Precel is a video journalist and reporter at The Age. She is also a documentary maker.