On identity: from a philosophical point of view

BACKGROUND: The term "identity" has a much longer tradition in Western philosophy than in psychology. However, the philosophical discourse addresses very different meanings of the term, which should be distinguished to avoid misunderstandings, but also to sharpen the key meanings of the term in psychological contexts. These crucial points in the philosophical concepts of identity in the sense of singularity, individuality, or self-sameness may structure the ongoing discussion on identity in psychiatric diagnoses (as in DSM-5, Child Adolesc Psychiatry Ment, this issue, 2013), in psychology, psychoanalysis, but also neuroscience and neurophilosophy (Child Adolesc Psychiatry Ment, this issue, 2013). METHOD: The concept of identity is subjected to a systematic philosophical analysis following some milestones in its history to provide a background for recent discussions on identity in psychiatry and psychology. RESULTS: The article focuses first on the philosophical core distinctions of identity in the different meanings to be addressed, second, briefly on some of the diverse psychological histories of the concept in the second half of the 20th century. Finally some reflections are presented on borderline personality disorder, considered as a mental disorder with a disturbance or diffusion of identity as core feature, and briefly on a newly developed instrument assessing identity development and identity diffusion in adolescence, the AIDA that is also presented in the special issue of this journal (Child Adolesc Psychiatry Ment, this issue, 2013). CONCLUSION: As a conclusion, different points of view concerning identity are summarized in respect to treatment planning, and different levels of description of identity in phenomenology, philosophy of mind, cognitive science, and social science and personality psychology are outlined.