From Carbon to Silicon: A Gradual Route to the Substrate Migration of Intelligent Agents

Conventional accounts of mind uploading typically envisage substrate migration through one-off scanning, copying, and reconstruction. Yet this model faces a fundamental problem of personal identity: a functionally equivalent copy does not automatically amount to the continued existence of the original subject. In response, this paper advances Gradual Neural Substrate Replacement as an alternative framework distinct from scan-and-copy logic. Its guiding idea is not to reconstruct, in another substrate, a system merely as similar as possible to the original subject, but to replace neural structures in stages so as to preserve the ongoing continuity of cognitive activity, neural function, and subjective experience within a continuously operating process. The paper argues that if the central issue in substrate migration is subject persistence rather than functional replication, then one-off uploading cannot by itself answer the question of who, if anyone, persists. On this view, the significance of gradual replacement should not be understood primarily as support for functionalism. It is better understood as an independent continuity-constrained pathway: by avoiding duplicative structure and preserving a non-branching process, it offers a stronger criterion of identity persistence. On this basis, the paper introduces the Subjective Experience Priority Principle, according to which stage-by-stage assessment should rely not on external functional performance alone, but on a joint evaluation of the subject's self-reports of continuity and objective cognitive testing. Drawing on the Ship of Theseus, theories of personal identity, and current developments in brain-computer interfaces, neural prosthetics, and language decoding, the paper analyzes the philosophical appeal, technical preconditions, and ethical complexity of gradual replacement in comparison with one-off uploading. It does not claim that gradual replacement is close to practical implementation, nor that it resolves every controversy surrounding subject migration. Its more cautious conclusion is that, within current theoretical and technological limits, gradual replacement bears more directly on the problem of subject persistence than scan-and-copy uploading and should therefore be treated as an independent and serious framework for research on substrate migration.