geared towards quick cheap labor for the PI's idea. I am not sure the phrase "quick cheap labour" really gets to the heart of the matter. The real reason why

geared towards quick cheap labor for the PI's idea. I am not sure the phrase "quick cheap labour" really gets to the heart of the matter. The real reason why most PhD students work on their supervisor's ideas is different. Most students would drown in the ocean of possible ideas, would simply fail without strong guidance from an experienced supervisor. It's probably best to see a PhD as a warm-up exercise for future research. The ocean of previous research one must master before being able to do original research in mature fields is simply so large that most students can't handle it on their own. Supervisors would love PhD-students who are intellectually mature enough to come up with their own ideas and execute them to a publishable standard. In my experience, at best 1 in 5 PhD students can do this. I used to think my own PhD work was 100% self-invented. But now, having supervised a lot of my own students, I see clearly how my intellectual mentor gently nudged me in the right direction at all critical junctions where I would have gone astray otherwise. Without him, I too would have failed. US PhD typically last a lot longer than UK PhDs, so comparing the two is difficult. I'd say UK PhD+postdoc is a probably comparable with an US PhD.