Copland did not consider himself a professional writer. He called his writing "a byproduct of my trade" as "a kind of salesman for contemporary music". As such, he wrote prolifically about music, including pieces on music criticism analysis, on musical trends, and on his own compositions. An avid lecturer and lecturer-performer, Copland eventually collected his presentation notes into three books, "What to Listen for in Music" (1939), "Our New Music" (1941), and "Music and Imagination" (1952). In the 1980s, he collaborated with Vivian Perlis on a two-volume autobiography, "Copland: 1900 Through 1942" (1984) and "Copland Since 1943" (1989). Along with the composer's first-person narrative, these two books incorporate 11 "interludes" by Perlis and other sections from friends and peers. Some controversy arose over the second volume's increased reliance over the first on old documents for source material. Due to the then-advanced stage of Copland's Alzheimer's and the resulting memory loss, however, this fallback to previous material was inevitable. The use in both books of letters and other unpublished sources, expertly researched and organized, made them what Pollack terms "invaluable".