 A philosophical understanding of intention (and thus not just Catholic doctrine) is needed to show that killing innocent people as a means to ending a war (or whatever) just is intentionally killing the innocent, despite whatever thoughts are running through the mind of the killer at the time. Thus she argues for a proper understanding of Aquinas’s idea that it matters whether some action’s effect is intended or merely foreseen, something we must grasp if we are to see what motivates the Principle or Doctrine of Double Effect (See SEP entry for more about the pros and cons of the Doctrine of Double Effect). Anscombe does not so much argue for the principle, as insist that it has not been adequately understood. So to defend the Principle of Double Effect, a principle of ethics, we first need a sound understanding of the concepts of action and of intention. More on this in Section 4.