  One consequence of this approach is that if the rationale for the earlier decision is tied exclusively to the particular category used in the ratio, there will be no scope for analogical extension to broader categories. In English law duress is not a defence to murder regardless of the circumstances, due (it is said) to the uniqueness of deliberate killing and the fact that duress is, at best, an excuse. On this rationale there is no room for arguing that duress should be excluded in cases of physically disabling a victim. On the question of whether duress could be a partial defence to murder, on the other hand, there is an arguable analogy to the excuse of provocation, which operates to reduce murder to manslaughter. Killing may be inexcusable, but that does not mean that every deliberate killing warrants a conviction for murder. Of course, duress involves an actual decision to kill, whereas provocation a temporary loss of self-control. The case for reducing killing under duress to manslaughter depends upon whether the rationale for provocation (e.g. as a concession to human frailty) extends to it. Two factors—the defendant's loss of self-control and the victim's involvement in the killing—readily distinguish the two situations, and weaken any analogy.