 Later treatments of this matter tend to disregard much of the complexity of this earlier approach for the reason that it fails to have any predictive power. Especially difficult to handle are “strengths”, for example. Modern models try to use update models instead (see Section 2.3 below). Van der Sandt 1991 uses a discourse model with three different slates (for each speaker, and one common slate). While each speaker is responsible for maintaining his own slate, changes to the common slate can only be made through communication with each other. Merin 1994 seeks to reduce the manipulations to a sequential combination of so-called elementary social acts: claim, concession, denial, and retraction.