List the elements of the doctrine of double effect and state when it is used

The doctrine of double effect comes to us from the philosopher St. Thomas Aquinas. The doctrine asks us to distinguish the intended effect of an action from other, unintended effects. This doctrine has been used to justify the death of fetuses under certain circumstances that threaten the life of the mother. Criteria for the doctrine of double effect include: the course chosen must be good or morally neutral; the good must not follow as a consequence of the secondary harmful effects; the harm must never be intended but merely tolerated as casually connected with the good intended; and the good must outweigh the harm.