I am a laymen of sorts in both physics and philosophy. I embarked on a trip to acquaint myself (gently at first) with contemporary physics. My question is foundational and therefore probably philosophical. If it is off-topic, please kindly point me to any place where such discussions may be held, but I prefer a material point of view. Basically, I have trouble understanding what "probability" means in QM. I have no hard objections to the hypothesis of physical non-determinism. What I cannot fathom is how one adapts the classical positivist attitude (like Occam's razor) into something useful while dealing with the Copenhagen interpretation. Let's say that the law of large numbers, central limit theorem, the Bayes' rule (, parameter estimates from sample statistics), etc. are metaphors for connections we believe exist between the human sense data (or human experience) and what we call probability. I assumed that we use probability to assign costs to outcomes and aggregate them to quantify a decision. A subjective, albeit constructivist process. I believed that it is used only as an epistemological device. QM introduces ontological probability. What does this mean for falsifiability? What is the notion into which falsifiability transforms and what are its observable virtues. For example, how would one introduce a concept such as Bayesian inference, as a verifiable physical reality? I cannot see the difference between probability and belief in the world view of QM. Is probability irreducible notion, and what is the sense data that "corresponds" to its manifestations? (I am not asking about non-determinism as physical reality, but the quantifiable non-determinism - the existence of probabilities directly in nature.) PS: I have tried to use the accepted terminology, but apologize if I have failed to do so.