A delineation of moral realism into a minimal form, a moderate form, and a robust form has been put forward in the literature. The robust model of moral realism commits moral realists to three theses:
The semantic thesis: The primary semantic role of moral predicates is to refer to moral properties, so that moral statements purport to represent moral facts, and express propositions that are true or false.
The alethic thesis: Some moral propositions are in fact true.
The metaphysical thesis: Moral propositions are true when actions and other objects of moral assessment have the relevant moral properties, where these facts and properties are robust: their metaphysical status, whatever it is, is not relevantly different from that of ordinary non-moral facts and properties.
The minimal model, i.e. moral universalism, leaves off the metaphysical thesis, treating it as matter of contention among moral realists. This dispute is not insignificant, as acceptance or rejection of the metaphysical thesis is taken by those employing the robust model as the key difference between moral realism and moral anti-realism. Indeed, the question of how to classify certain logically possible views—such as the rejection of the semantic and alethic theses in conjunction with the acceptance of the metaphysical thesis—turns on which model we accept. Someone employing the robust model might call such a view "realist non-cognitivism," while someone employing the minimal model might simply place such a view alongside other, more traditional, forms of non-cognitivism. The robust model and the minimal model also disagree over how to classify moral subjectivism. The historical association of subjectivism with moral anti-realism in large part explains why the robust model of moral realism has been dominant—even if only implicitly—both in the traditional and contemporary philosophical literature on metaethics. In the minimal sense of realism, R. M. Hare could be considered a realist in his later works, as he is committed to the objectivity of value judgments, even though he denies that moral statements express propositions with truth-values per se. Moral constructivists like John Rawls and Christine Korsgaard may also be realists in this minimalist sense; the latter describes her own position as procedural realism. Some readings of evolutionary science such as those of Charles Darwin and James Mark Baldwin have suggested that in so far as an ethics may be associated with survival strategies and natural selection then such behavior may be associated with a moderate position of moral realism equivalent to an ethics of survival.
Advantages
Moral realism allows the ordinary rules of logic to be applied straightforwardly to moral statements. We can say that a moral belief is false or unjustified or contradictory in the same way we would about a factual belief. This is a problem for expressivism, as shown by the Frege–Geach problem. Another advantage of moral realism is its capacity to resolve moral disagreements: if two moral beliefs contradict one another, realism says that they cannot both be right, and therefore everyone involved ought to be seeking out the right answer to resolve the disagreement. Contrary theories of meta-ethics have trouble even formulating the statement "this moral belief is wrong," and so they cannot resolve disagreements in this way.
Proponents
adopts a moral realist position, criticizing Stevenson's idea that when evaluation is superposed on fact there has been a "committal in a new dimension." She introduces, by analogy, the practical implications of using the word "injury." Not just anything counts as an injury. There must be some impairment. When we suppose a man wants the things the injury prevents him from obtaining, haven’t we fallen into the old naturalistic fallacy? Foot argues that the virtues, like hands and eyes in the analogy, play so large a part in so many operations that it is implausible to suppose that a committal in a non-naturalist dimension is necessary to demonstrate their goodness.
Criticisms
Several criticisms have been raised against moral realism. The first is that, while realism can explain how to resolve moral conflicts, it does not explain how these conflicts arose in the first place. The widespread disagreement about what is right and wrong is puzzling if humans are assumed to have access to moral facts. The evolutionary debunking argument suggests that because human psychology is primarily produced by evolutionary processes which do not seem to have a reason to be sensitive to moral facts, taking a moral realist stance can only lead to moral skepticism. This undercuts the motivations for taking a moral realist stance, namely to be able to assert there are reliable moral standards. Others are critical of moral realism because it postulates the existence of a kind of "moral fact" which is nonmaterial and does not appear to be accessible to empirical investigation. Moral truths cannot be observed in the same way as material facts, so it seems odd to count them in the same category. However, such an argument may be applicable to our concepts of epistemic justification as well, possibly leading to radical skepticism and thus threatening to undercut the moral anti-realist's argument. This criticism is also not applicable to ethical naturalism, a form of moral realism which suggests the possibility of a science of morality by considering moral claims to be referring to observable entities.
