Irving Berlin and Cole Porter were two of the great experimental songwriters of the Golden Era. They aimed to create songs that were clear and universal. Their ability to do this improved throughout much of their careers, as their skill in using language to create simple and poignant images improved with experience, and their greatest achievements came in their 40s and 50s. During the 1960s, Bob Dylan and the team of John Lennon and Paul McCartney created a conceptual revolution in popular music. Their goal was to express their own ideas and emotions in novel ways. Their creativity declined with age, as increasing experience produced habits of thought that destroyed their ability to formulate radical new departures from existing practices, so their most innovative contributions appeared early in their careers.
This is the abstract of David Galenson's new paper on the two creativity patterns in songwriting. Extremely interesting, very convincingly argued, and at the same time a crash course into the musical biographies of Berlin, Porter, Dylan, Lennon and McCartney. See also a previous entry on Galenson's research.