Under the circumstances where various uncertainties exist, such as the remarkable escalation of natural phenomena including global warming in recent years, there is an increasing need to consider events beyond the scope of assumption in the design of civil engineering structures. Here, an attempt to classify the relationship between assumed events in design and various events beyond the scope of assumption based on the degree of perception of uncertainty is described. By rationally dividing these two phenomena in the design, it became possible to implement measures to increase robustness and redundancy on the boundary on a scenario basis as a structural plan. Furthermore, it has also become possible to clarify the positioning of anti-catastrophe, which encompasses the assumed events and the events beyond the scope of assumption.