The "Non-Aggression Axiom" is the least controversial component of libertarian doctrine. Simply put, libertarians will not employ physical force in order to advance their interests, except in self-defense. Keep in mind that physical aggression is subject to degrees ranging from a gentle push to the use lethal weapons. This moral committment to non-aggression extends to libertarian political beliefs as well. How much aggression can I justifiably employ under what kinds of circumstances? What does self-defense mean? Well, it clearly involves both rights and duties. It indicates that libertarians acknowledge that they have a duty to NOT employ physical force, unless others employ it first. In short, I will use physical force to protect myself. Unfortunately, there is a grey area here. What can a libertarian do when other parties threaten to employ physical force, but have not yet actually employed it? In other words, under the non-aggression axiom, is preemption ever justified? I have serious reservations when it comes to preemption. Threats are subject to personal interpretation. Sometimes we interpret the behavior of others as threatening based on misinformation or disinformation. And sometimes others threaten to use physical force, but really have no intention of doing so. Unfortunately, when we employ physical force preemptively in order to ward off an imagined threat, we can expect others to seek out retribution. This invariably leads to tit-for-tat cycles of retribution. We might invoke the concept of an immanent threat as justifcation for the use of physical force. If you walk into my home at night with a gun drawn, would I be justified in shooting you as an act of preemption? As far as I am concerned, it would depend on the availability of other non-lethal options. The best way to conceptualize libertarianism's committment to non-aggression is to assume that our default moral position is peace. However, do not interpret our committment to peaceful non-aggression as an invitation to employ physical force against us. If neccessary, we can be very efficient in the art of self-defense.