The first class wanted the PhD as a means to an end, such as doing research, or getting a professorship. The second class had more abstract and less well-define

The first class wanted the PhD as a means to an end, such as doing research, or getting a professorship. The second class had more abstract and less well-defined goals. Sometimes that meant generally "doing good for the world", or "seemed like the right thing to do", or "the working world sucks, this is the lesser of two evils". I agree with your subdivision, but I'd add another class: people who want to understand/solve/think-about some hard problem they find genuinly interesting and who don't particularly care about career as an academic, or the good of the world or anything much else, they just want to think about this topic because they enjoy it and grad school gives them a relatively stable environment where they can do it.