How can we tell right actions from wrong ones? The best interpretation of Kant’s Universal Principle of Right establishes a dual test for the rightness of actions, corresponding to the two distinct types of wrong actions that Kant describes elsewhere: formal wrongs and material wrongs. Because we have a right to do anything that is not wrong, formal wrongs and material wrongs should collectively exhaust the category of conduct that the Universal Principle of Right excludes. Material wrongs are actions that violate the innate or acquired rights of another free agent. Formal wrongs are actions that violate “the right of human beings as such” to live in a rightful condition. The application of traditional common law doctrines to simple examples demonstrates that the wrong-making property of a material wrong is a property of an action’s “outer form,” while the wrong-making property of a formal wrong is a property of the action’s maxim – its principle of inner determination. The dual nature of wrongdoing complements my textual argument in favor of a two-standard interpretation of the Universal Principle of Right. Finally, I suggest that the meaning of Kant’s principle may be obscured by a typographical error.