In this article, I discuss what I call “the problem of otherness” in dissociative identity disorder, which addresses the extent to which we validate and recognize the perception of otherness in each part of personality (PP) regarding other PPs. The general trend is considered to not fully validate it, which seems to stem from the era of the Freud–Janet controversy, partly due to the conceptual ambiguity of the splitting of the mind in the sense of division vs. multiplication. Consequently, we tend to consider dissociation as a defensive and intentional act, at least when it was initiated, with an understanding that PPs are not structurally separated from each other, but are rather internally and dynamically connected to each other, and that a PP is somewhat causative to and responsible for another PP's thoughts and behaviors. Here, I consider the hypothetical neurocognitive model that is based on the “dynamic core” model proposed by G. Edelman, where the neurological correlate of dissociative identity disorder is conceived as a simultaneous and multiple existence of a “dynamic core”, which represents each PP as a unique and wholesome existence in the conscious.