Relational quantum mechanics is still incompatible with quantum mechanics [1]

We showed in a recent article (Lawrence et al. 2023 [5]. Quantum, 7, 1015), that relative facts (outcomes), a central concept in Relational Quantum Mechanics, are inconsistent with Quantum Mechanics. We proved this by constructing a Wigner-Friend type sequential measurement scenario on a Greenberger-Horne-Zeilinger (GHZ) state of three qubits, and making the following assumption: “if an interpretation of quantum theory introduces some conceptualization of outcomes of a measurement, then probabilities of these outcomes must follow the quantum predictions as given by the Born rule.” Our work has been criticized by Cavalcanti et al. (2023 [6]. European Journal for Philosophy of Science, 13(4),55). In this note we show that their critique, based on their own reformulation of our argument, does not apply to our paper. It also raises questions of principle which are not answered within the framework of Relational Quantum Mechanics.