This article attempts to improve the understanding of the heterogeneity between bipolar and unipolar depression based on the work of Karl Abraham in 1924. To achieve this goal, this article presents the reasons for choosing Karl Abraham as a starting point for interdisciplinary research and going through his 1924 work, summarising his contributions to the psychopathology and psychogenesis of depression and the limitations of his findings, namely, that although he proposed a theoretical model with Freudian dynamics and an empirical basis, he failed to recognise the differences between bipolar and unipolar depression due to the limitations of his time. Nevertheless, his model still retains a certain clarity that continues to offer us valuable clues. Therefore, under this triaxial model of the developmental stages of libido, object love, and the Oedipus complex, this article proposes to distinguish neurotic depression, bipolar depression, and unipolar depression through the inscription or non-inscription of the Oedipus complex and the integrity or nonintegrity of the ego.