Warren contrasts theories of moral status which are uni-criterial with those that are multi-criterial. A uni-criterial theory of moral status takes the view that there is some single criterion that we can use to determine what the moral status of a particular entity is. Various philosophers have proposed various uni-criterial theories of moral status. Kant's view that take rational agency as the sole criterion of intrinsic moral value, and hence moral status, is one example. Other people have proposed that genetic humanity is the proper criterion. Peter Singer, and other utilitarians have proposed that sentience, in particular, the capacity for pain and pleasure, functions as the sole criterion. Still others take other things such as self-consciousnsess or being the "subject of a life" as providing the criterion for moral status. Others, like Albert Schweitzer, propose that life or being alive is the criterion for having moral status.
But Warren argues that none of these uni-criterial theories of moral status can adequately account for the full range of our considered moral intuitions about cases calling for moral discrimination and judgment. Her view, which I find to be convincing is that "any satisfactory account of moral status must be a multi-criterial one, comprising a number of distinct but related principles" (20-21). In particular, Warren argues that:
(1) there is more than one valid criterion of moral status; (2) that there can be more than one type of moral status, with different types involving different obligations on the part of moral agents; and (3) that the criteria of moral status must include both certain intrinsic properties, including life, sentience, personhood, and certain relational properties, which sometimes include being part of a particular social or biological community. (21)Like Warren, while I think that it would be nice to have a simpler theory of moral status, it is preferable to have one that is more descriptively adequate and which can account for a wider range of robust moral intuitions that competent moral judges have about cases calling for moral discrimination and judgment found in our current commonsense morality. Theories of moral status, however, should not be expected to satisfy everyone's opinions on these matters. Theories and principles are important in normative ethics because they help us correct our biases and guide our judgment in borderline cases. Theory choice in normative ethics is determined by a number of factors other than simplicity and descriptive adequacy alone, so it does not follow that just because a theory of moral status is "simple" or accounts for a number of current moral intuitions, it is correct. Ultimately, any theory of moral status will have to be discursively legitimized and translated into moral and in some cases legal norms that function to guide the judgment and action of large numbers of human moral agents. Philosophers, like Warren and myself, can only point the way towards such socially legitimized norms, we cannot by writng down our thoughts and reasons create them.
Warren does an excellent job in her book of giving philosophical arguments against the various uni-criterial theories of moral status. I am not going to spend a lot of time here rehearsing her arguments, but suggest that the interested reader consult her work. Since I agree with her general approach, I am going to save some time by jumping right into her own multi-criterial theory of moral status. It is, I believe, the best available account of its kind and so can provide a good starting place for further philosophical development.
The goal of this inquiry, recall, is to provide an account of what I am calling "moral patients", that is, those things which can function as the objects of our moral responsibilities. It is necessary to provide such an account in order to determine the boundaries of the moral community for which, I believe, we need an ethics of global responsibility.