The Born rule — the axiom that measurement probability equals |ψ|² — has resisted derivation from deeper principles since 1926. This paper proposes that it is not an axiom but a consequence of the coherence condition. A measurement outcome is realized if and only if it preserves the coherence of the combined system-observer state: K (S+O) > Kcrit. The Born weight |cᵢ|² is identified as the coherence preservation measure — the fraction of the joint Hilbert space norm available for coherence maintenance in branch i. Outcomes with low |cᵢ|² are not improbable; they are incoherent — the resulting system-observer state lacks the temporal structure required for observation. This resolves the measurement problem without collapse, without branching, and without hidden variables: only coherent branches have observers, and only observers have outcomes. Falsifiable prediction: Born rule deviations at experimentally degraded observer coherence, testable with existing quantum optics apparatus. Part of the Spektre research corpus.
Lauri Elias Rainio (Sun,) studied this question.