 For various reasons, after the discovery of quantum mechanics it quickly became almost universal to speak of an experiment associated with an operator \(A\) in the manner just sketched as a measurement of the observable \(A\)—as if the operator somehow corresponded to a property of the system that the experiment in some sense measures. It has been argued that this assumption, which has been called naive realism about operators, has been a source of considerable confusion about the meaning and implications of quantum theory (Daumer et al. 1997a).