"Don't hurt people and don't take their stuff" is a famous libertarian adage (and book by Matt Kibbe) that simplifies the philosophy.
Force includes, but is not limited to:
- Violent Assault
- Theft
- Rape or Sexual Assault
- Trespassing
- Damaging Private Property
- Wrongful Imprisonment
- Slavery
- Murder
Certain types of force may never be used. However, permeating academia and intellectual circuits, the libertarian debate of when and how force may be applied rages on. The NAP is controversial--even amongst libertarians, but they acknowledge its vital points and generally adhere to the principle.
For more information, see What is Libertarianism?