Thirteen hundred years have passed since the birth of Western Europe’s great musical tradition. Gregorian chant, first heard in the eighth century, is mother to a miraculous offspring including motets, cantatas, sonatas, operas, concertos, and symphonies, but perhaps most miraculous, the most unlikely of all her children, is the 19th-century German “Lied,” translated literally, “song.” The life of her remarkable child spanned hardly more than a century; Ludwig van Beethoven, Franz Schubert, Robert Schumann, Johannes Brahms, Hugo Wolf, and Richard Strauss, produced their songs and then fell silent, leaving no significant progeny. Of course, people have been writing songs since writing came about, and people continue to do so. But the phenomenal outpouring of great music in this genre, songs generally for one voice with piano or occasionally orchestral accompaniment, is unprecedented, matchless, a miraculous phenomenon in our cultural history. Perhaps the expanded role of the piano is its most remarkable …