The Practical, Physical (and Sometimes Dangerous) Consequences of Control Must Be Respected, and the Underlying Principles Must Be Clearly and Well Taught

F eedback control systems are all around us in modern technological life. They are at work in our homes, our cars, our factories, our transportation systems, our defense systems—everywhere we look. Certainly, one of the great achievements of the international controls research community is that the design principles for these systems are well developed and broadly understood by control engineers, so that the systems operate productively and safely in so many applications. In this article, I want to talk about two trends that threaten to undermine this achievement. My objective is to heighten our awareness of these trends and hopefully bring about an appropriate response to them. The first trend has to do with the applications themselves. Among the abundance of control systems operating today are increasing numbers of dangerous ones. Society trusts our technology. We are permitted to do things with automatic controls that cannot be done manually and that, if done improperly, can have dire consequences for property, the environment, and human life. Most, but not all, of these dangerous applications involve open-loop unstable plants with divergence rates violent enough to elude manual control. This characterization motivates the title of the article, and I will describe specific examples of such applications. The second trend has been evident at our conferences, and certainly in our journals, over the years. This trend is the increasing worship of abstract mathematical results in control at the expense of more specific examinations of their practical, physical consequences. I will provide examples of this trend as well.