Parity Principle
Clark's criterion for the Extended Mind thesis, stated verbatim in the source: "if, as we look at some cognitive task, something is going on outside the head such that if it were inside the head we'd regard it as cognitive, then until proven otherwise we should give it the benefit of the doubt and count it as cognitive." Its load-bearing clarification is what the standard objection misses: the principle demands parity of opportunity, not parity of process. "Your iPhone doesn't work like your brain — where's the parity?" is a misreading; the external element need not operate on the brain's principles, only play the role. It presupposes just a "coarse functionalism" — what you can do in the world, how fluently, and when — not any stronger philosophical functionalism.
For the vault, this is the clean test for when an external store has crossed from tool to part of the system: judged by role, not by mechanism — an agent's markdown memory doesn't need to resemble weights or a context window to count as its memory.
Claims
- If an external process, were it inside the head, would be regarded as cognitive, count it as cognitive until proven otherwise. (principle — as asserted by Clark)
- The parity is of opportunity, not of process: no requirement that the external element work like the brain; the "iPhone doesn't work like a brain" objection misreads the principle. (principle — as asserted by Clark)
- The principle needs only coarse functionalism (capability, fluency, availability), not the strong functionalism some philosophers reject. (observation — Clark's framing of the commitment)
- "There's no privileged border of the skin and the skull when it comes to the mind — what matters is the role" a state plays; a phone storing your numbers plays a role "precisely analogous" to the biological memory it replaced. (principle — Chalmers's independent wording of the same criterion, in the sibling interview; two sources now state the role-not-mechanism test)
- The parity principle alone is too weak: unsupplemented, it would extend the mind until "almost the entire world becomes part of the mind" — everything in an old encyclopedia in the shed would qualify. In that source's telling, parity is criterion 1 of 4, supplemented by the Extended Mind Criteria (typically invoked, trustworthy, easily accessible). (principle — as asserted by the Tilburg University explainer, attributed to Clark & Chalmers; the insufficiency point is new to the vault — neither author interview raised it)
Related
- Extended Mind — the thesis this principle operationalises.
- Cognitive Scaffolding — the structures the principle admits into the cognitive system.
- AI Second Brain — role-not-mechanism is why plain files count as memory: the test is "can it find it again?", not whether the store resembles a brain.
- Extended Mind Criteria — the supplementary conditions (typically invoked, trustworthy, easily accessible) that answer the principle's over-admission problem.
- Distillate: Andy Clark — What is Extended Mind? (Closer To Truth)
- Distillate: David Chalmers — What is Extended Mind? (Closer To Truth)
- Distillate: The Extended Mind Hypothesis (Tilburg University explainer)