Consider the constrained part (denoted as the plant) of a control system, consisting ofncascaded sections, each of whose outputs can be sensed for feedback purposes. Feedback from these points is to be used to achievea priorispecified tolerances on the system response, despite great uncertainty in plant parameter values. In this first quantitative work of its kind, the feedback is permitted to proceed directly to internal plant variables, constituting ‘ plant modification ’. The reason is that the internal plant signal levels needed to achieve a specific output are now affected by the feedback loops. This is in contrast to previous quantitative research in which the feedback was confined to the plant input. The plant signal levels needed to achieve a specific output were then not influenced by the feedback.