Ethical theory often starts with our intuitions about particular cases and
tries to uncover the principles that are implicit in them; work on the ‘trolley problem’
is a paradigmatic example of this approach. But ethicists are no longer the only ones
chasing trolleys. In recent years, psychologists and neuroscientists have also turned
to study our moral intuitions and what underlies them. The relation between these
two inquiries, which investigate similar examples and intuitions, and sometimes
produce parallel results, is puzzling. Does it matter to ethics whether its armchair
conclusions match the psychologists’ findings? I argue that reflection on this question
exposes psychological presuppositions implicit in armchair ethical theorising. When
these presuppositions are made explicit, it becomes clear that empirical evidence can
(and should) play a positive role in ethical theorising. Unlike recent assaults on the
armchair, the argument I develop is not driven by a naturalist agenda, or meant to cast
doubt on the reliability of our moral intuitions; on the contrary, it is even compatible
with non-naturalism, and takes the reliability of intuition as its premise. The argument
is rather that if our moral intuitions are reliable, then psychological evidence
should play a surprisingly significant role in the justification of moral principles.
