Under the IHL framework, the reasonableness standard is traditionally resorted to in the determination of the possible excessiveness of the expected incidental harm with the concrete and direct military advantage anticipated, i.e. during the proportionality assessment. The analysis carried out in the present chapter aims at challenging this narrow view, by arguing that this standard is a transversal one that could, and should, inform the application of all the other IHL principles, i.e. distinction, precautions, military necessity, and humanity (or unnecessary suffering), both during military actions in general and in the specific case of attacks against dual-use objects. As the standard is far from well-settled, this chapter will first provide the reader with a thorough overview of the theoretical underpinnings of reasonableness, and then it will discuss it in combination with each of the key IHL principles. The goal is to define the contours of the “reasonable military commander standard” in a more precise way and detail how it unfolds in the process of targeting dual-use objects. The findings of this chapter ultimately show that there is a sliding scale in the application of the reasonable standard that potentially allows both the actors and those who review the actions undertaken to operate with greater certainty.