The identification which occurs here is, as we can see, nothing other than a mode of thinking.[3] The question was taken up again psychoanalytically in Ferenczi's article, 'Introjection and Transference', dating from 1909,[4] but it was in the decade between On Narcissism (1914) and The Ego and the Id (1923) that Freud made his most detailed and intensive study of the concept.