Epistemology is the study of knowledge and justified belief. So moral epistemology is the study of what would be involved in knowing, or being justified in believing, moral propositions. Some discussions of moral epistemology interpret the category of ‘moral propositions’ broadly, to encompass all propositions that can be expressed with terms like ‘good’ or ‘bad’ or ‘ought’. Other discussions have focused on a narrower category of moral propositions – such as propositions about what rights people have, or about what we owe to each other.
According to so-called noncognitivists, one cannot strictly speaking know (or be justified in believing) a moral proposition in the same sense in which one can know (or be justified in believing) an ordinary factual proposition. Other philosophers defend a cognitivist position, according to which it is possible to know or be justified in believing moral propositions in the very same sense as factual propositions.
If one does know any moral propositions, they must presumably be true; and the way in which one knows those moral truths must provide access to them. This has led to a debate about whether one could ever know moral truths if a realist conception of these truths – according to which moral truths are not in any interesting sense of our making – were correct.
Many philosophers agree that one way of obtaining justified moral beliefs involves seeking ‘reflective equilibrium’ – that is, roughly, considering theories, and adjusting one’s judgments to make them as systematic and coherent as possible.
According to some philosophers, however, seeking reflective equilibrium is not enough: justified moral beliefs need to be supported by moral ‘intuitions’. Some hold that such moral intuitions are a priori, akin to our intuitions of the self-evident truths of mathematics. Others hold that these intuitions are closely related to emotions or sentiments; some theorists claim that empirical studies of moral psychology strongly support this ‘sentimentalist’ interpretation.
Finally, moral thinking seems different from other areas of thought in two respects. First, there is particularly widespread disagreement about moral questions; and one rarely responds to such moral disagreement by retreating to a state of uncertainty as one does on other questions. Secondly, one rarely defers to other people’s moral judgments in the way in which one defers to experts about ordinary factual questions. These two puzzling features of moral thinking seem to
demand explanation – which is a further problem that moral epistemology has to solve.