The accompanying variation method says that if we find in a number of situations leading to a particular effect, a certain property of the effect, which varies with the variation in a factor common to these situations, then we can deduce this factor as cause. As is the case, we are interested in examining cases where the effect is present and learning more about the properties that exist and are missing under the « possible necessary conditions ». Obviously, the missing properties when the effect is present cannot be necessary conditions of action. This method is also described in comparative policy in general as the most diverse conception of the system. .