“Tomorrow the birds will sing. Love David.” Thumbed onto an iPhone by David Hockney in 2009, printed onto a magnet, sold near the exit of an art gallery, purchased and then placed by me at eye level on my refrigerator at home, next to a postcard of The Dream by Henri Rousseau. I read these words every day. The magnetised avowal is a reproduction of hundreds of little iPhone drawings that Hockney draws in his Brushes app, which he then texts to his friends every morning. His favourite thing to...