Identity as Admissibility Boundary: A Structural Account of Persistence Across Change

Accounts of persistence across change typically specify what content is identity-constitutive, whether psychological relations, biological continuity, or narrative coherence. This paper argues that such accounts presuppose an unspecified structural condition: a persistence-relative admissibility boundary governing what difference may enter a system and what difference is excluded. Identity at this level is defined by exclusion rather than internal content. The paper argues further that admissibility at this boundary is binary. A difference either enters the governing configuration of the system or it does not. On that basis, the paper defines identity drift as categorical boundary violation, argues that drift cannot be repaired by downstream dynamics alone, and specifies explicit conditions under which the account would be refuted.