Recent studies at the interface of social cognition and personality theory have stressed lay persons' ability to ‘function as intuitive psychometricians’ (Epstein and Teraspulsky, 1986). This research argues that lay persons not only show a substantial degree of accuracy in estimating cross-situational generality of behaviour, but also take into account principles of aggregation over time. In contrast, it is argued here that lay persons' perceptions of the degree of relatedness of different behaviours are mediated largely by the decontextualized semantic relationships between behavioural descriptions. This argument finds support in two experimental studies which demonstrate that the main source for subjects' judgments of ‘cross-situational consistency’ can be found in an abstracted knowledge base which is represented and mediated through language. The implications of the findings are drawn out for personality research, in particular with reference to domain and item selection in questionnaires for research.