 The foregoing considerations are all also relevant to necessity. They allow us to weigh the harms at stake, so that we can determine whether the morally weighted harm inflicted can be reduced at a reasonable cost to the agents. The basic structure of necessity is the same in bello as it is ad bellum, though obviously the same differences in substance arise as for proportionality. Some reasons apply only to in bello necessity judgements, not to ad bellum ones, because they are conditional on the background assumption that the war as a whole will continue. This means that we cannot reach judgements of the necessity of the war as a whole by simply aggregating our judgements about the individual actions that together constitute the war.