the assignment of quantum states as *constitutive rules* in the sense of [@Searle]. Section 3.2.2 extends it to an account of quantum probabilities and the Born Rule.

Quantum Bayesianism
-------------------

The central idea of quantum Bayesianism is that quantum probabilities, as encoded in quantum states via the Born Rule, are *subjective* probabilities in the subjective Bayesian sense. As such, they are construed as reflecting the state assigning agents’ subjective degrees of belief as to what the results of their future “interventions into nature”[^12] might be. Degrees of belief may legitimately differ from agent to agent without any of them behaving irrationally or making any kind of mistake. So, from the quantum Bayesian point of view different agents may indeed legitimately assign different quantum states to the same system, no notion of a quantum state as a state some quantum system “is in” is employed, and the position qualifies as a potentially consistent epistemic account of quantum states. According to Fuchs, “quantum states do not exist”[^13] in that they are not part of the furniture of the world. They do not correspond to any physical facts or properties of physical system but, instead, represent the assigning agents’ degrees of belief as 