Is it still the same river if every drop of water has been replaced?

@Invisible: The river does not have a conscience, it is pure matter.
We are no only matter, our conscience does not change if we get a kidney transplant. It is a change, but not an essential one.

If a man gets a brain lesion and can no longer speak, is he the same man? He can think all the same

@Invisible: I don't think we are totally the same we were a second ago.
I would not call that person a different one, since he can think all the same. However, if braon transplant was possible, someone would be a different person when receiving a new brain.

@theowl: Isn't it every 7 years all our cells are replaced by new cells? Or is it longer?

it might be 7 i was told a decade back when i took human anatomy a little over a decade ago.