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According to this article, it looks like there's not a significant difference between the ThD and the PhD, at least at Duke. You have access to pretty much all of the same profs and courses. So, continuing to use Duke as an example, if you were drawn there because of the professors, there would be no reason to prefer the PhD over the ThD other than the "prestige," real or imagined, of graduating from a Graduate Program rather than a Divinity Program. But lets face it, a degree from Duke is a degree from Duke. Same would go for any of the top-tier programs that offer ThD's.