Political philosophy — the libertarian philosophy included — can take you only so far. The libertarian philosophy provides grounds for condemning aggression, that is, the initiation of force, and along with some supplemental considerations, it identifies in the abstract what constitutes aggression, victimhood, and self-defense. But the philosophy can't identify the aggressor and victim in particular cases; relevant empirical information is required, and we cannot apply the theory of justice without empirical information. No ethical or political theory can answer empirical questions, yet they are critical to applying the theory in order to determine who was the aggressor and who was the victim. The same would be true, writes Sheldon Richman, if we observed an unarmed person shot dead in the street and another person nearby holding a smoking gun, even if the man with the gun is a white member of a police force and the dead person is a young black man who had no weapon.