A principle attempting to define when an action that has both good and bad results is morally permissible. In one formulation such an action is permissible if

1. (i) the action is not wrong in itself,

2. (ii) the bad consequence is not that which is intended,

3. (iii) the good is not itself a result of the bad consequence, and

4. (iv) the two consequences are commensurate.

Thus, for instance, I might justifiably bomb an enemy factory, foreseeing but not intending the death of nearby civilians, whereas bombing the civilians intentionally would be disallowed. The principle has its roots in Thomism. Its applications include the problem of removing (thereby killing) a life-threatening foetus. All the clauses of the definition are highly controversial, but the second especially gives rise to deep problems about the relation between action, consequence, and intention. The principle is often explored via examples such as the Trolley problem.