Editor,— The editorial by Paolo Vineis1 is an interesting attempt to clarify various interpretations of causality in the medical literature. The following remarks are to be taken as a mere running commentary of the excellent paper by Vineis.

Causation is a conditional relation such as: if C then D. Ventricular standstill causes death: if the ventricles fails to contract, the patient dies.

What binds causes to their effect? Counterfactual conditionals (or counterfactuals) introduce some sort of necessity in a causal relation. Counterfactuals have the following structure:

Assuming that (1) If C then D and (2) C and D occur.

then we have: If C had not occurred (though it did), D would not have occurred.

Counterfactuals are conditionals that are contrary to the facts as the first part of the conditional “if C had not occurred” is false. Counterfactuals translate into predictions and introduce some support of necessity that allows to separate statements that are accidentally true from those which are regularly true: in the second case, our knowledge extends to the counterfactual cases.

Incidentally, I have serious reservations about the usefulness of Hempel's or Popper's hypothetico-deductive models because there are no such things as general laws in medicine: medical explanation is not deductive.

Vineis distinguishes five major interpretations of causality in medicine. After discussing an earlier broad Aristotelian one he brings in a second stream, springing from the success of bacteriology and according to which causality is analysed in terms of agency: a cause is a single, necessary factor of its effect. If C is a necessary cause of D, than D necessitates C in each way of maintaining other causal or interacting factors constant. A necessary factor is a sine qua non determinant on which the effect depends; it usually involves a cause-effect relation of …

Professor Porta (e-mail: mporta{at}imim.es)