Interlevel relationships should not be accepted as causal relations.

The debate here quickly gets into technical arguments about the concept of causation. Campbell argues against Frith in favour of the Humean idea that we simply cannot tell in advance of inquiry what causal relations obtain in nature. Anything can cause anything and it is just as unwarranted to suppose that the relevant explanatory variables for psychotic or affective phenomena must be cognitive as it is to adopt a simple reductionism and insist on their being biological. Decades of research have