Gordon Parker makes a powerful case against the hypothesis that borderline personality disorder is really a form of bipolar or unipolar disorder. Reference Parker1 In so doing he is tilting at a windmill in whose construction I had absolutely no part. In my article Reference Tyrer2 and in other critiques Reference Tyrer3,Reference Tyrer4 I do not claim any connection between bipolar, unipolar and borderline: I only state that borderline personality disorder has far greater affinity to mood than to personality. Its core is not a disorder of depression or mania, but one of emotional dysregulation associated with many other mood states; Reference Reisch, Ebner-Priemer, Tschacher, Bohus and Linehan5 nothing about it is driven by personality. The very name ‘borderline personality disorder’ betrays an abrogation of diagnosis. It overlaps with post-traumatic stress disorder, other personality disorders, anxiety, depression, and dissociative and adjustment disorders, yet does not belong to any of them. By having layer upon layer of diagnostic requirements that allow it to become grossly heterogeneous, it has confused everybody and satisfied none. Personality disorders are trait based and these traits are persistent over time and linked to normal personality variation. There is good evidence that borderline-personality characteristics are closely linked to affective instability, not normal personality variation, Reference Kendler, Myers and Reichborn-Kjennerud6 and its natural history is one of remission rather than persistence. Reference Zanarini, Frankenburg, Hennen and Silk7 The task of nosology is now to separate the essential core of emotional dysregulation from personality disorders, where its infiltration has been most damaging, Reference Mulder, Crawford and Tyrer8 and from the many disorders that give the term ‘comorbidity’ such a bad press. A start has been made in the reclassification of personality disorder in ICD-11, where borderline personality disorder and the other current categories of personality disorder have all been removed, Reference Tyrer, Crawford and Mulder9,Reference Tyrer, Crawford, Mulder, Blashfield, Farnam and Fossati10 but much more needs to be done.