Sometimes it is morally permissible to prevent someone from performing a wrongful act by harming him before he has a chance to act. It is permissible, for example, to kill someone you reasonably fear is about to kill you. Under other circumstances, however, it may only be permissible to threaten to harm someone to discourage him from performing a wrongful act. It is not always permissible straightaway to harm him. A military commander, for example, may threaten an enemy with disproportionate retaliation, even though it would not ordinarily be permissible to carry it out.