Mental representations of possibility in everyday contexts incorporate descriptive and prescriptive norms. People intuitively think that Mr X cannot perform an immoral action; even when upon deliberation they realise that the immoral action is in fact possible. We test how context affects mental representations of possibility by asking whether the same findings hold in a war context. This context has different prescriptive norms (e.g., it is permissible to kill people, but not innocent people), and we propose a study using a reaction-time paradigm to test whether these prescriptive norms shape people’s representations of what is possible in war. The proposed study will advance our understanding of the relationship between morality and domain-general cognition, and provide insight into the moral landscape of war.