How to Interpret the QBist Constraint

This paper refines and applies the QBist constraint, which holds that consciousness requires an irreducibly first-person, self-updating inferential structure. Inspired by Quantum Bayesianism (QBism), the constraint is framed not as a positive theory of consciousness, but as a metatheoretical adequacy condition applicable across candidate frameworks. I argue that theories of consciousness — including the Free Energy Principle, Predictive Processing, Global Workspace Theory, Higher-Order Thought Theory, and Integrated Information Theory — can be evaluated against this constraint. The paper shows how each theory may either accommodate or fall short of satisfying this demand. I close by suggesting that the QBist constraint serves as a useful delimiting principle for theories of consciousness, helping to clarify the role of subjectivity in physicalist models.