Rep36 Understanding Personality Disorder

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evaluated separately (Hill, Fudge, Harrington,
Pickles & Rutter, 2000).
1.1.8 Classification of personality disorders
and clinical practice
Trait description is a starting point for clinical
understanding of personality disorders, but the
limitations of traits in predicting and explaining
individual behaviour need to be recognised.
Whatever the advantages of dimensional
representation, both categories and dimensions
are essentially abstractions that provide no more
than a global guide to dysfunction. While traits
provide summary descriptions of behaviour, they
do not explain behaviour because the causes of
the trait-relevant behaviour remain to be
identified.
Philosophers recognise a distinction between
dispositional concepts that denote frequency of
behaviour given certain conditions and those that
are ‘purposive-cognitive’(Alston, 1975). The
former are close to the conventional meaning of
trait and refer to surface regularities in behaviour.
They predict probabilistically, but do not explain.
The latter refer to ‘deep’ structures and processes
posited by theory that are not directly observable
but provide a more fundamental causal
explanation of behaviour (e. g. motives, schemas,
defences, coping mechanisms). Similar
distinctions are made by psychologists between
surface (phenotypic) and source (genotypic)
traits. There is therefore more to personality than
surface traits, and source or genotypic traits are
the more basic constituents of personality. 
Theoretical models developed to guide
treatment of personality disorder are concerned
primarily with ‘purposive-cognitive’ dispositions
rather than the surface traits defining personality
disorder (Section 2.1). Attempts to improve the
classification of personality disorder by reference
to the structure of personality traits have
therefore had only a limited impact on strategies
for treating these disorders. An integration of
trait description and theoretical constructs of
personality is crucial if the classification of
personality disorder is to assist clinicians.