The preferred basis is causal: The measurement problem in an ontology of actualization

The "preferred-basis problem" — why does measurement produce definite outcomes in this basis rather than another — is treated in opposite ways by the interpretations of quantum mechanics: posited ab initio (spontaneous collapse), drawn from a contingent environment (decoherence), left to the choice of a framework (decoherent histories), avoided (many-worlds, pilot wave). We show that in the Time–Actualization ontology — where measurement is an instance of the universal process of actualizing quantum potentialities into events — the preferred basis is anchored in the causal past of the event, together with a readiness condition: which events that past has made ready to actualize. TA does not introduce a new selection mechanism: it identifies the environment of einselection with the already-actualized causal past — an environment that is not posited outside the formalism (unlike an external classical apparatus), but is part of the same substrate. The causal location of this environment is foliation-independent; its monitoring content depends on the couplings, not on the bare order alone. Covariance of the associated operations requires the locality hypotheses stated below. The uniqueness of outcomes is posited, not explained. Born's rule remains imported, and empirical equivalence with quantum mechanics on the causal-set substrate is a requirement still to be verified for a complete dynamics. The contribution is ontological and local to the preferred-basis question. A symmetric downstream mechanism — the redundant proliferation of the outcome into the causal future (quantum Darwinism) — in addition accounts for the inter-observer objectivity of the actualized fact, without deriving it.