Why be moral? This question is fundamental for ethics, because even if people can figure out what
are the right things to do, we can still ask why they would in fact do those things. The problem of
moral motivation—what makes people do what is right—has two classes of answers, rationalist and
sentimentalist. The traditional philosophical responses to the problem have been rationalist: we
should be moral because it would be irrational to do otherwise. The rationality of morality might
derive from a priori truths about what is right, or from arguments that it is rational for people to agree
with others to be moral. The philosopher Sean Nichols argues that a major problem for rationalism is
that psychopaths, with no impediments in abstract reasoning, nevertheless see nothing wrong in
harming other people.