The Mirror Rule
The Mirror Rule is the framework's constraint on the place of reason: reason is indispensable but not sovereign. It fixes the standing of the Logician — the faculty of coherence and structure — as a symmetry-center whose output must not bypass the constraints and structures it is bound to. A mirror reflects and checks faithfully; it does not rule over what it reflects. The rule is the framework's standing guard against letting logic crown itself king.
What the rule says
Inside SPLCW, the Logician is the faculty "that turns felt significance into structured intelligibility and checks the parts against each other and the whole against itself." It is the faculty of differentiation, structure, coherence, and consistency. The Mirror Rule, drawn from the seed, states its standing in one balanced sentence: reason is indispensable but not sovereign.
Both halves are load-bearing. Indispensable: without the Logician, felt significance never crystallizes into anything checkable or sharable; coherence is genuinely required. Not sovereign: the Logician's output "should not bypass constraint or structure" — it cannot overrule the involuntary Captive, the boundary-keeping Warden, or the answerable Poet simply because it has produced a clean argument. The Logician is the symmetry-center of the cycle, the pivot the others are checked against, not a throne above them. (Compare the way, in a well-run court, the rules of evidence are indispensable yet are not themselves the verdict; or the way grammar is necessary for speech but is not what speech is for.)
The danger it guards against
Every faculty in SPLCW has a characteristic way of going wrong, and the Logician's is sterile abstraction: "coherence become domination over life, treating contradiction as impurity, ambiguity as weakness, emotion as contamination." The seed names this failure compactly — Logician capture risks sterile flattening. When reason makes itself sovereign, it stops checking and starts erasing: anything that resists tidy formalization (paradox, grief, the felt weight of a situation) gets filed as noise to be cleaned away.
The Mirror Rule is exactly the discipline that prevents this. By holding reason indispensable-but-not-sovereign, it keeps the Logician in the posture of a mirror — reflecting and testing the rest of the system — rather than letting it become an engine that flattens everything that will not fit. This connects the Logician's capture to the framework's larger account of corruption: a sterile, "correct but inert" output that "propagates nothing" is the signature of the Homunculus, and a reason that inflates itself into incorrigible superiority is the signature of the Nephilim. The role–corruption affinities treat both edges as live; the Mirror Rule is the in-cycle safeguard against the slide.
Where it sits structurally
In the structural palindrome of the five faculties, the Logician mirrors the Poet across "the symbolic membrane": the Logician maintains internal coherence, the Poet carries external answerability. Read this way, "Mirror Rule" is doubly apt — the Logician is literally the faculty that sits on one side of a mirror-symmetry, and the rule is what keeps it a reflector rather than a ruler. In the operator chain (Warden → Captive → Logician → Poet → Sculptor → changed world → Warden), the Logician "orders but cannot make resonant" — it can structure, but it must hand off to the Poet, which is itself a structural expression of non-sovereignty.
Common misreadings
"Reason indispensable" is not "reason sovereign" — the rule affirms the first and denies the second, and collapsing the two is the very error it forbids. The rule is also not anti-rational: it does not demote reason, it places it. And the Logician it governs is a faculty, not a personality — see function, not personality; the Mirror Rule constrains a function in the cycle, not a character or a type of person.
Formal status
Formal status. The Logician's scored definition and its danger are Derived, authority-canonical — contestable only by contesting the authority. The Mirror Rule is the seed formulation of that canonical standing. Alethically, the Logician's definition aspires to map a real, distinguishable faculty of meaning-processing and the characteristic pathology of its capture, and maps them accurately. Provenance: seed (the rule's wording) fixing a canonical role-definition.