There is a curious parallel between the philosophy of science and psychiatric theory. The so-called demarcation question, which has exercised philosophers of science over the last decades, posed the problem of distinguishing science proper from non-science - in par- ticular, from metaphysics, from pseudo-science, from the non- rational or irrational, or from the untestable or the empirically meaningless. In psychiatric theory, the demarcation question appears as a problem of distinguishing the sane from the insane, the well from the mentally ill. The parallelism is interesting when the...