Carl Porter Duncan (December 27, 1921 – August 9, 1999) was a professor of experimental psychology at Northwestern University. Carl P. Duncan was born on December 27, 1921, in Presque Isle, Maine. His father, Henry Beecher Duncan, was a farmer and his mother Vivian Howlett Duncan, a schoolteacher. Duncan met his wife, Marie Castaldi, while at Brown University, and they were married in 1948. She received her doctor of medicine degree in 1951, and practiced in adolescent psychiatry. They had no children. Duncan suffered a fatal fall on August 9, 1999, while trimming a tree.