ABSTRACT
This paper attempts to explain the strange phenomenon whereby the central problem of plant uncertainty in feedback control theory was almost totally ignored for about four decades. Furthermore, Quantitative Feedback Theory (QFT) which did concentrate on this central problem was ignored. It is suggested that there were two principal motivational sources of feedback theory: the transcontinental telephone line and the radar fire-control system. A genuine engineering theory of feedback was developed by the former in the context of feedback amplifiers. However, the second was inherently constrained as a one degree-of-freedom structure which severely limited the design theory objectives. Later generations of researchers accepted the limited objectives, even the underlying constraints were not applicable.
