Let X be some idea. Is X effective? We could mean two different things by this. First, X is a project—a system of rules for governance, both individual and collective. X, privately, tells the individual what to do; publicly, it tells the collective what to do. Is this program, properly executed by individual and/or collective, effective? If so, X is an effective idea—an idea that believes in having good effects. If not, it is not. Second, X itself is a tool for changing the world.