Considering various arguments in Hume’s Treatise, I reconstruct a Humean argument against personal identity or unity. According to this argument, each distinct perception is separable from the bundle of perceptions to which it belongs and is thus transferable either to the external, material reality or to another psychical reality, another bundle of perceptions. Nevertheless, such transference (Hume’s word!) is entirely illegitimate, otherwise Hume’s argument against causal inference would have failed; furthermore, it violates private, psychical accessibility. I suggest a Humean thought (...) experiment clearly demonstrating that, to the extent that anything within a psychical reality is concerned, no distinction leads to separation or transference and that private, psychical accessibility has to be allowed in the Humean argument for personal identity or unity. Private accessibility and psychical untransferability secure personal identity and unity. Referring to the phenomenon of multiple personality along the lines of the Humean argument for personal identity or unity, I illustrate both private accessibility and a possible notion of one and the same person distinct from his/her alters or psychical parts. Finally, I show why Parfit’s Humean argument against personal identity must fail. (shrink)