Lehnert (1980) proposed a model thematic knowledge structures called 'plot units', which are structurally deflned sequences of mental states, positive events, and negative events In a clustering experiment, subjects were asked to sort 36 stories into groups. These groups were labeled by the subjects, and that data used to identify the nature of each mental category. Plot units generally provided a good fit to the clustering patterns in the data, with higher level clusters corresponding to discriminations on the nature of the outcome and judgements about the 'fairness' of the protagonist.