With the type of music he began to write at this time, he needed tonality for the music to work. He didn't necessarily need harmony. Consideration of harmony came only later because of a drone phenomenon that occurred when the Philip Glass Ensemble were playing Music with Changing Parts in an auditorium with a curious accoustic. It was unintentional harmony. It prompted Glass to think about harmony and the music, style, and experimentation that he was working on. "Another Look at Harmony Parts 1-4" is exactly what it says it is: it's another look at harmony. After about five years, Glass was taking another look at how ideas about harmony fit into his music. Parts 1-3 of the series were later incorporated into Einstein on the Beach. Part 4, which I will hear this Sunday in New York, is the only surviving stand-alone piece.