This paper was prepared for submission to the Insight magazine of the International Council on Systems Engineering (INCOSE) Proactive and Reactive Resilience: A Comparison of Perspectives Scott Jackson 1,2 Timothy L. J. Ferris 2 1 Burnham Systems Consulting – Greater Los Angeles 2 University of South Australia Abstract This paper reviews two perspectives of the concept of resilience found in the literature. The traditional perspective found in the fields of ecology, psychology, and materials science views resilience as a reactive quality pertaining to the encounter with a disturbance and for the period following the disturbance. Researchers studying engineered systems, that is, systems for which human involvement is required to assure recovery, have introduced the concept of proactive resilience. These researchers use the three-phase model of disruptions in which design rules, such as drift correction, are active before, during, and after the encounter. Hence, reactive resilience only considers the inherent resilience of the person, object, or other entity being analysed since no human involvement is required. Definitions of resilience from the proactive perspective contain words such as anticipate and plan to describe activities that occur before the disturbance. Researchers in the defense community sometimes use the reactive perspective to describe resilience as part of a larger concept of survivability. Another driver for the proactive perspective is the phenomenon of dependency. The authors found in a previous paper that vulnerabilities inherent in some resilience design rules, when implemented, required the application of one or more additional design rules to compensate for these vulnerabilities. For example, the selection of a design rule pertaining to the period following the encounter may require a second design rule to be applied to the period before the encounter. Thus design rules are required to cover all three phases. The final conclusion is that neither the reactive nor the reactive perspective of resilience is correct or incorrect. A researcher may adopt either perspective depending on the context of the analysis providing that the analysis is rigorous. 1.0 Introduction An observer will find in the literature two perspectives with regard to the concept of resilience. One perspective can be called the reactive concept. In this concept resilience refers to an inherent property of a person, object, or other entity that allows it to recover from a disturbance. This is the traditional view of resilience. In more recent years, however, a broader view of resilience has emerged in which activities before the disturbance are included. These activities define how the object anticipates and plans for the disturbance and how the object might avoid or reduce the effect of the disturbance. This is called the proactive view of resilience. So the questions might