The absence of a due good, i.e., a privation of a good that should be present. 

Moral Evil.— The absence of correspondence between an action, a principle of actions, or effects of actions and the natural moral law. For example, murder is morally evil because it fails to correspond to what is required by the natural moral law. 

Natural Evil.— The absence of some form that is naturally perfective of a thing. For example, sight is perfective of the power of sight since eyes are naturally inclined to see. Blindness, which is the absence of sight, is, in this respect, bad for the power of sight.