<p>Early social development exhibits a qualitative transition: children move from predicting and coordinating with others to treating certain regularities as binding standards that license correction, protest, and third-party enforcement. This paper proposes that the transition is driven by symbolic closure, a stabilization operation through which pre-symbolic social coupling and practice participation yield deontically binding representations. Normative bindingness is defined as the emergence of scope-sensitive invariance in a child’s deontic evaluation map: stability under perturbations that preserve a norm’s legitimate scope, paired with principled divergence at scope boundaries. Bindingness is operationalized as a perturbation profile of deontic stability and summarized by a compact Normative Closure Index (NCI), defined as one minus the expected divergence of deontic evaluations under task-relevant perturbations. This formulation recasts established developmental paradigms, joint pretense and game norm enforcement, authority contingency, group membership manipulations, monitoring and incentive shifts, and third-party perspective probes, as structured tests of perturbation profiles rather than isolated endorsement measures. The framework yields testable predictions, including domain-by-perturbation dissociations that express the moral–conventional distinction as differences in invariance class, and a developmental pattern in which within-scope stability increases and then plateaus while boundary sensitivity is preserved. Symbolic closure thus provides a minimal perturbation grammar for identifying when and how “what people do” becomes “what one ought to do,” while remaining compatible with multiple learning routes.</p>