Is it wrong to cite your own definition of a concept in thesis viva-voce presentation

Question

Recently, I defended my PhD thesis in the final viva-voce session. Post the presentation, one of the panel members questioned that I should not have stated my own definition of a particular concept. The panel member suggested that I should have rather given a industry-standard definition for that particular concept.

This makes me think and wonder that Why I should not suggest my own definition of the concept. After all the definition was published by an high impact journal and has been cited many times. By the way, I understand what they meant. And my PhD supervisor too did not raise this as a concern when I sent them the presentation for checking.

My contention here is, I have worked in this area for several years and I do not get the right to cite my definition for my own viva.

Answer 1

In other countries, the viva-voce is called "defense" for a reason. The onus is on you to defend your use of the definition, in particular, if it deviates from the industry standard.

Answer 2

In this type of question, context is everything, and so it's hard to give an unequivocal answer. That being said:

I'd in general have no trouble with someone, in a Ph.D. defense, article, whatever, giving their own definition of a concept, as long as they demonstrated an awareness of what the more standard definitions are, and articulated why it is beneficial to deviate. In fact, a discussion of what the standard definition(s) miss and why the presenter's definition is either preferable, or at least provides an enriching if temporary detour, might be a great structuring device for summarizing what's novel about the results anyway.

I would have trouble with someone just asserting a novel definition of a term with established usage, but not engaging with more standard definitions. To the extent they are an apprentice scholar (e.g. student "defending"), it would make me wonder if they have sufficiently "done their homework" to place their contribution in the corpus of established research in the field. Were they unaware of the other definition(s) and/or did they miss crucial nuance? And to the extent they are now fellow independent research practitioners (and the Ph.D. is the inflection point for this, of course), redefining terms and making it stick invariably generates confusion in the field, so should not be done lightly. And the onus is on the one suggesting a terminological change to be crystal clear what the change is (and why). And whether it's fair or not, the bar for that is higher for someone new to the field than someone already well-established.