 Ethicists as diverse as Kant (1971/1797), Mill (1979/1861), and Ross (1930, 1939) have assumed that an adequate moral theory should not allow for the possibility of genuine moral dilemmas. Only recently—in the last sixty years or so—have philosophers begun to challenge that assumption. And the challenge can take at least two different forms. Some will argue that it is not possible to preclude genuine moral dilemmas. Others will argue that even if it were possible, it is not desirable to do so.