Writing music takes more talent, but writing lyrics takes more courage.                       —Johnny Mercer Now that Bob Dylan, a singer-songwriter, has won the Nobel Prize for Literature, it is hard to imagine a time not long ago when the writing of popular songs was a specialised activity, quite distinct from the business of singing them. Songwriting was traditionally a collaboration between two craftsmen: a lyric writer and a music composer. Singers never wrote their own material. Between the 1920s and the 1950s, in the days before pop charts and video clips, popular music was dominated by a canon of songs…