R. M. Hare's "two-level utilitarianism"
we have "moral intuitions that lead us to do what will bring about the best consequences in the situations we encounter" but that we also find ourselves occasionally in "an extraordinary situation in which [acting counter to these intuitions] would bring about consequences good enough to clearly outweigh any bad consequences that might [result]"
Joshua Greene's "evolutionary argument"
explains some odd results when studying the trolley problem
(people think it is OK to throw a switch to kill one person, but not to push someone directly on the tracks)
Greene concludes that "we have a strong intuition against using hands-on violence to kill someone, even to save more lives [...] He suggests that this is because hands-on violence has been possible for the entirety of our existence as human beings. Without an inhibition against it, perhaps even in our ancestral social primages, the small communities in which we lived would not have survived. Trolley switches, on the other hand, have not existed long enough to have evolved an intuition against using them to kill"
John Rawls' "reflective equilibrium" -- we test "normative moral theories against one's own moral intuitions and [revise] both until they are in accord, or as close as possible"
all summations from Peter Singer, in NYRB