Roy Weintraub has made a very important point when reminding us about Sidney Weintraub's use of C+I and not "IS". Indeed, the original diagram as presented by Hicks had a CC (MEC) schedule and not SI . The original Harrod-Meade-Hicks equational and diagramatic system underwent many changes from its original nominal income- interest rate framework to what became the "trained intuition" of many, but not all economists, as Roy points out... On these and related points, see Young (1987) and Darity and Young (1995)... Warren Young