The kind of necessity which 'chc(E)=l' must express is usually if not always contingent: it can exist in our world without existing in all other possible worlds and so cannot be metaphysical necessity [1.6]. Don's falling must be able to necessitate his dying in our world without doing so in all worlds, or even in all worlds where he falls in circumstances which are relevantly similar (except that the laws of nature may differ). Not even total causes must need to necessitate their effects in all possible worlds in order to necessitate them in ours.