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Context: Some believe that Requirements Engineering (RE) for a computer-based system (CBS) should be done up front, producing a complete requirements specification before any of the CBS’s software (SW) is written. Problem: A common complaint is that (1) new requirements never stop coming; so upfront RE goes on forever with an ever growing scope. However, data show that (2) the cost to modify written SW to include a new requirement is at least 10 times the cost of writing the SW with the requirement included from the start; so upfront RE saves development costs, particularly if the new requirement is one that was needed to prevent a failure of the implementation of a requirement already included in the scope. The scope of a CBS is the set of requirements that drive its implementation. Hypothesis: We believe that both (1) and (2) are correct, but each is about a different category of requirements, (1) scope …