Turtles All the Way Down: Regress, Priority and Fundamentality

I address an intuition commonly endorsed by metaphysicians, that there must be a fundamental layer of reality, i.e., that chains of ontological dependence must terminate: there cannot be turtles all the way down. I discuss applications of this intuition with reference to Bradley's regress, composition, realism about the mental and the cosmological argument. I discuss some arguments for the intuition, but argue that they are unconvincing. I conclude by making some suggestions for how the intuition should be argued for, and discussing the ramifications of giving the justification I think best.