The debate about pluralism in morality is rather different—it is a debate about a structural issue, and does not have implications for whether a theory is relativist, objectivist, or subjectivist. One could be a pluralist and an objectivist or realist, and one could also be a pluralist and a non-realist. The question about whether values are plural or monist is a question about the shape of morality—in particular, about how many values moral theory must deal with.Moral pluralism is not about different value systems or viewpoints, but about different values. Commonsensically we talk about lots of different values—happiness, liberty, friendship, and so on. The question about pluralism in moral theory is whether these apparently different values are all reducible to one super value, or whether we should think that there really are several distinct values. There are different ways that value might be conceived, but the debate about pluralism should be able to cut across different sorts of moral theory. Traditionally, moral philosophers recognize three different ways of thinking about morality: the consequentialist way, the deontological way, and the virtue ethics way, although there is debate about the cogency of these distinctions
The deontologist usually sees value differently, talking in terms of rules and principles rather than in terms of goods. The pluralism issue arises for the deontological approach to value: is there a plurality of principles, or is there one over-arching principle? Kant can be understood as a monist—arguing that there is one overarching principle, and that all other principles are derived from it. Ross, by contrast, is a pluralist, because he thinks that there is a plurality of prima facie duties. (See Kant (1948), Ross (1930).)
Monists claim that there is only one ultimate value. Utilitarians, for example, usually argue that there is only one value and that is welfare or pleasure or happiness, or something of that ilk. Monist utilitarians must claim that all other putative values, such as friendship, knowledge and so on, are only instrumental values—valuable in so far as they contribute to happiness. Pluralists argue that there really are several different values, and that these values are not reducible to each other or to a super value. Monism has the advantage of relative simplicity—once it has been determined what the super value is (whether we think of the super value in terms of the goods approach or any other approach) much of the hard work has been done. On the other hand, monism may be too simple—it may not capture the real texture of our ethical lives. However, pluralism faces the difficulty of explaining how different fundamental values relate to each other, and how they can be compared.