Discussions of diagnosis in mental illness are still beset by the suspicion that ‘value judgements’ are in some special sense ‘subjective’. The history of the debate about the reality of mental illness has seen a divide between those who accept that diagnosis is ‘value-laden’ and therefore accept a relativist/subjectivist account of mental illness, and those who feel the need to deny the value-laden nature of diagnosis to defend the reality of mental illness. More nuanced analyses note that (a)all medical diagnosis (...) is arguably value-laden & (b)this does not imply that medical conditions are unreal. All judgement (about value or fact) requires a subject, but it does not follow that it is ‘subjective’ in any sense implying ontological relativity. The implications are substantial: either all medical judgement is relative (a thesis we argue is counter-intuitive and deeply problematic) or realism about value is true. To justify our claims in diagnosis, we need to discuss and defend our value-judgements. We must reject ‘scientism’ for an openly value-laden account of human functioning. Medical epistemology (including the epistemology of mental illness) requires value-realism. The contentious nature of the value-judgements in the case of mental illness should not mislead us into concluding they are relative. (shrink)