Idem, an alius? On Substitution, the Masks of Continuity, and the Seam Dressed as a Passage

What distinguishes genuine change from substitution? This essay develops the companion problem to Quid est mutatio?. If change is the becoming-otherwise of one numerically continuous subject — the same, otherwise — substitution is its counterfeit: replacement, A → B, presented under the grammar of change, A₁ → A₂. The essay examines resemblance, sequence, memory, name, causal descent, and persisting function as ordinary signs of continuity that may remain persuasive without establishing the persistence of the bearer. Genesis 27 supplies the epistemic scene of the problem: Isaac encounters the signs of one subject gathered around another. The algorithmic case sharpens the distinction, since computational succession alone cannot decide whether a substrate persists, is replaced, or is conventionally renamed. The final sections turn to answerability, arguing that judgement, promise, authorship, and repentance presuppose a continuous subject. The governing question is therefore not whether the signs continue, but whether the subject does: idem, an alius? — the same one, or another?