Original: The libretto, written by W. H. Auden and Chester Kallman, is based loosely on the eight paintings and engravings A Rake's Progress (1733 - 1735) of William Hogarth, which Stravinsky had seen on May 2, 1947, in a Chicago exhibition.
Simplified: The libretto written by W. H. Auden and Chester Kallman is based loosely on the eight paintings and engravings from the 18th century by William Hogarth called A Rake's Progress. Stravinsky had seen these paintings in 1947 at an exhibition in Chicago.