There is a widespread assumption among both policy makers and members of the general public that more resources should be poured into the prevention of psychological disorders. This view is frequently accompanied by the parallel assumption that the knowledge required to set up effective preventive programs is already available. The problem, it is supposed, lies in inertia and vested interests to keep things as they are (Keniston & Carnegie Council on Children, 1977; Segal, 1975). After all, there is a wealth of evidence on the variables associated with all manner of psychological disorders. Surely, this gives us a good enough appreciation of the causal features; all that remains is the task of designing interventions to impact on those features and then test which form of intervention works “best.” That scenario would involve a fair number of practical difficulties but, at least, the general way forward would be clear.

However, the picture is a seriously misleading one (Rutter, 1982). The issues involved in gaining an adequate understanding of causal mechanisms are much more complicated than generally appreciated. The question of what is the basic cause of any psychological disorder, or indeed any social circumstance, is far from straightforward.

This is not a matter of ivory tower academic niceties; rather it is central to the whole enterprise of prevention and intervention, whatever the target of concern. If we are to be able to devise effective measures, it is essential that we appreciate the complexities inherent in concepts of causation.