What constitutes as an adequate justification for use of an operational definition within a model is subjective indeed. However there is usually a point in the

What constitutes as an adequate justification for use of an operational definition within a model is subjective indeed. However there is usually a point in the life of a theory where the gathered evidence are sufficient enough that a scientific consensus starts to form that the operational definition is justified. I’m not aware that that has happened in the 40-odd year history of the Big 5 personality theory. The 5 personality traits may be overarching within the field of psychometrics and they may indeed be useful to describe behavior, however you still need to justify that said behavior is not easier described using different models, and this is where personality psychologists usually fails in justifying their operands. Works criticizing the model range from using totally different constructs (such as priming, positive reinforcement, universal grammar, brain dopamine level socio-economic status etc.)—which don’t rely on psychometrics at all—to claiming that the behavior psychometricians are predicting are actually not that useful (e.g. predicting ‘high confidence’ is not that useful if ‘high confidence’ does not result in a significant behavior which isn’t better predicted without made up operands). If you were an early astronomer and you constructed the notion of ‘epicycles’ to simplify your model of planetary motion. You may use these ‘epicycles’ to justify your prediction, however you may not use a successful prediction to justify the existence of epicycles. Your epicycles may be useful until someone comes along and deems them unnecessary since planetary motion is better described by using elliptical orbits. Of course this could go the other way as is the case with particle physics and the atom. However given the amount of research, success of rival theories, the failure of psychometricians from making useful predictions outside of their narrow field that isn’t better explained with alternative theories, I have high doubts that the Big-5 personality traits (and any theory of personality using psychometrics for that matter) is anything but pseudoscience.