For a long time, it seemed that Aristotelians and Kantians had little to say to each other. When Kant the moralist was known in the English-speaking world primarily from his Groundwork and his Critique of Practical Reason, Kant's conceptual vocabulary of “duty,” “law,” “maxim,” and “morality” appeared quite foreign to Aristotle's “virtue,” “end,” “good,” and “character.” Yet ever since philosopher Mary Gregor's Laws of Freedom, published in 1963, made Kant's The Metaphysics of Morals central to the interpretation of his ethical thought, it has become clear that such “Aristotelian” terms as virtue, end, good, happiness, and character are also central to Kant. Aristotelians and Kantians now see that they have plenty to say to each other, and they have gone from being adversaries to sharing a sometimes unprincipled urge to merge central aspects of Aristotle's and Kant's ethical thought.

Epistemology, as I understand it, is a branch of philosophy especially concerned with general questions about how we can know various things or at least justify our beliefs about them. It questions what counts as evidence and what are reasonable sources of doubt. Traditionally, episte-mology focuses on pervasive and apparently basic assumptions covering a wide range of claims to knowledge or justified belief rather than very specific, practical puzzles. For example, traditional epistemologists ask “How do we know there are material objects?” and not “How do you know which are the female beetles?” Similarly, moral epistemology, as I understand it, is concerned with general questions about how we can know or justify our beliefs about moral matters. Its focus, again, is on quite general, pervasive, and apparently basic assumptions about what counts as evidence, what are reasonable sources of doubt, and what are the appropriate procedures for justifying particular moral claims.

How many serious mistakes can a brilliant philosopher make in a single paragraph? Many think that Mill answers this question by example—in the third paragraph of Chapter IV of Utilitarianism. Here is the notorious paragraph:

The only proof capable of being given that an object is visible, is that people actually see it. The only proof that a sound is audible, is that people hear it: and so of the other sources of our experience. In like manner, I apprehend, the sole evidence it is possible to produce that anything is desirable, is that people do actually desire it. If the end which the utilitarian doctrine proposes to itself were not, in theory and in practice, acknowledged to be an end, nothing could ever convince any person that it was so. No reason can be given why the general happiness is desirable, except that each person, so far as he believes it to be attainable, desires his own happiness. This, however, being a fact, we have not only all the proof which the case admits of, but all which it is possible to require, that happiness is a good: that each person's happiness is a good to that person, and the general happiness, therefore, a good to the aggregate of all persons. Happiness has made out its title as one of the ends of conduct, and consequently one of the criteria of morality.