Commentary: positivized epidemiology and the model of sufficient and component causes.

dialogue form obliges the reader to consider the discussants' relationships to each other and to the author. In Karhausen's dialogue on Rothman's model of sufficient and component causes (SCC) (e.g. ref. 1, pp.7–17) in this issue of the International Journal of Epidemiology 2 these relationships are complicated by the fact that the participants—Socrates and Epimenide—are historical figures to whom historically questionable statements have long been attributed. Socrates' role in Plato's dialogues is a matter of perpetual uncertainty. Russell found it 'very hard to judge how far Plato means to portray the historical Socrates, and how far he intends the person called " Socrates " in his dialogues to be merely the mouthpiece of his own opinions'. 3 We have no such difficulty with Karhausen's Socrates. 2 He speaks for Karhausen as unambiguously as Salviati spoke for Galileo in another dialogue patterned on the Platonic form. 4 Rothman has written favourably on epidemiological applications of some of Popper's ideas (e.g. ref. 1, pp.18–19), but Karhausen abhors 'Popperian epidemiology'. 5 So Karhausen's Socrates, 2 a crafty argumentarian and his master's faithful servant, takes every opportunity to turn Popper against Rothman. Karhausen employs Epimenide roughly as Galileo employed Salviati's foil Simplicio: as a dimwit barely familiar enough with established dogma to give a garbled account of some of its more obvious features. This imbalance makes Karhausen's dialogue read much as Feyerabend's second dialogue on knowledge read to Feyerabend: 'not really a dialogue but a diatribe directed at a helpless victim'. 6 The historical Epimenide was a Cretan alleged to have said that all Cretans are liars. If a liar is one who never tells the truth, he had to be lying and at least one Cretan had to tell at least one truth. Ironically, as we shall see, the less than honest discussant in Karhausen's dialogue 2 is not Epimenide, but Socrates. A flawed model among many Karhausen's characters discuss the SCC model as though it were the only causal model in epidemiology. 2 They seem blissfully unaware of others, especially counterfactual models (ref. 1, pp.60–62), 7–9 whose developers are well on their way to discerning exactly what is needed for association to equal causation. Like the SCC model, all these causal models have limitations. They must. They are only models. Some of the SCC model's limitations are inherent. As a model for aetiological mechanisms, it is too 'deep' to serve as a …