"I Know Why (And So Do You)" is a 1941 song by Glenn Miller and His Orchestra. The song appeared in the 20th Century Fox movie Sun Valley Serenade. The song was also released as an RCA Bluebird 78 single.
Background
The song was written by Mack Gordon, lyrics, and Harry Warren, music. The song is lip-synched by Lynn Bari in the movie Sun Valley Serenade. Pat Friday sang the vocals with John Payne and The Modernaires. The single, RCA Bluebird B-11230-A, reached no. 18 on the Billboard pop singles chart in a one-week chart run.[1] The single release featured vocals by Paula Kelly and The Four Modernaires. The B side of the single was "Chattanooga Choo Choo" which, de facto, was treated as the A-side.
The tune was the one being rehearsed in the film, The Glenn Miller Story, when Jimmy Stewart was pretending to be Glenn Miller, trying to invent a new sound; then the trumpeter hurt his lip, which caused Miller to substitute a clarinet, creating the new sound.
The 1941 Glenn Miller recording was featured in the 1990 Warner Bros. movie Memphis Belle and the 2017 film The Shape of Water which was nominated for 13 Academy Awards. It also was played at Ginger Rogers' party early in the 1954 movie "Black Widow."
The version used in the 1941 film Sun Valley Serenade features lead vocals by Pat Friday (and a verse by star John Payne) once again backed by The Modernaires.
Album appearances
The song appears on the following albums:
Remember Glenn Miller, 20th Century, 1973
The Complete Glenn Miller, Vol. 6 (1940-1941), RCA Bluebird
Glenn Miller: The Popular Recordings (1938-1942), RCA Bluebird, 1989