I think I've cleared up a fundamental misunderstanding I've had for a while, and want to get confirmation I'm right. Is the following statement true? In QFT, a quantum field is not part of the state of a quantum system, and is not an aspect of reality that needs to be measured to be known. Instead, the field is known a priori, and instead is (a field of) observables that one may measure about the quantum system. I had been confused on this point since in classical mechanics, fields were always part of the physical system. Then, when I see quantum field being defined as operators -- especially with emphasis on the resemblance to wave-functions -- I was confused because the formalism only provides for measurements to be done on a state space, not on an operator algebra! But now I realize "the value of the field at a point" is being treated as an observable (like position in OQM) rather than as an aspect of the quantum state, and things now start to make more sense. I just want to make sure this is the right kind of sense before I start molding my understanding to it.