Aiming at the perceptual evaluation of virtual acoustic environments (VAEs), 'plausibility' is introduced as a quality criterion that can be of value for many applications in virtual acoustics. We suggest a definition as well as an experimental operationalization for plausibility, referring to the perceived agreement with the listener's expectation towards a corresponding real acoustic event. The measurement model includes the criterion-free assessment of the deviation from this non-explicit, inner reference by rating corresponding real and simulated stimuli in a Yes/No test paradigm and analyzing the results according to signal detection theory. The specification of a minimum effect hypothesis allows testing of plausibility with any desired strictness. The approach is demonstrated with the perceptual evaluation of a system for dynamic binaural synthesis in two different development stages.