The Non-Aggression Principle, or NAP, is one of the key phrases in libertarianism. It is “an ethical stance which asserts that aggression is inherently illegitimate.” Most libertarians in the general movement are aware of the principle and either explicitly abide by it, or implicitly do. The principle has been criticized from various angles over the years. For example, does it apply to a fetus? to a nonhuman animal? And what if you see someone tipping over a train platform, can you grab them and pull them back? You have aggressed against them, but it was to prevent harm from coming to them.
Awhile ago, I derived an idea that a good way to boil down libertarianism is to take the golden rule and make it a negative. The golden rule states “Do unto others as you would want done unto you.” I stated “Do not do unto others as you would not want done unto yourself.” Apparently, this concept already existed, and is known as the silver rule. Hillel the Elder is reputed to have made such a statement to a prospective convert. However, it does not appear to have gained much traction in libertarianism. To me, it makes a better guiding principle. It explicitly permits an intervention on your behalf (most people would not want someone to not help them out, even if it involved force against themself), even if it is an aggressive behavior. I would hope that someone would prevent me from injuring myself even if they had to initiate some force against me. Certainly, not everyone must agree with this, however, it is important to have alternatives to the NAP and look at the general concept of aggression, force, coercion and limiting it severely in different ways.