The elements or basic ingredients of music are defined. Musical excerpts from Episode 3 return. Other featured pieces are Mozart's "Piano Sonata, K. 545"; Bach's "Little Prelude in D, BWV 936"; Rachmaninoff's "Symphony No. 2"; Mendelssohn's "Symphony No. 4, 'Italian'" and Morton Subotnick's "Silver Apples of the Moon" - as well as a bit of humor - are all used to refine these definitions.