A note on campbell's distinction between internal and external validity

The concepts of internal and external validity, developed by Norman Campbell, are widely used to structure methodological thinking about social research. This article points to ambiguities in the interpretation of those terms, both as regards the relationships they refer to as well as the sort of object that is held to be capable of internal and external validity. In addition, it is suggested that the distinction between these types of validity is fundamentally misleading because it reflects a failure to distinguish relations between events and relations between variables. It also rests on the false assumption that we can separate the discovery of causal relationships from the question of whether these apply to other cases than the ones studied. In the final section, an alternative conceptualisation of validity is sketched, one that avoids the problems identified.