 Categorical substitutability involves a negative and a positive condition. These are necessary and jointly sufficient for obligability. The negative condition says that the agent’s willing of a certain action was not completely determined by the nomic and singular conditions which existed at the time of willing. Not surprisingly, Broad regards an action that merely fulfils this condition as “an accident, lucky or unlucky as the case may be.” Neither the agent nor “anything else in the universe can properly be praised or blamed for it” (1934, p. 212; Broad’s italics).