“Moral realism” is the proposition that objective moral rules exist. A moral rule assigns a moral value (good, evil, or neutral) to an act done by a person. A moral rule, such as “theft is evil,” is intended as a fact.
Moral realism is non-nihilist and non-relativist. Nihilists and relativists believe that no act is inherently good or evil, that there is no morality beyond personal and cultural beliefs. Moral realism is based on an ontology, a way to show that an objective morality exists.
The existence of an objective and universal ethic cannot be based on intuition. Intuition consists of ideas believed without conscious thinking. What people think of as intuition is heavily influenced by the prevailing culture. One person’s intuition may tell him that gambling is bad, while other may think that gambling is harmless fun.
Many ontologies of morality have been proposed. The one I think is warranted in reason is the natural moral law proposed by John Locke, although he did not present a derivation. In my judgment, the ontology consistent with Locke is as follows.
1. There are criteria that are necessary for the existence of a universal ethic. The ethic has to be universal to all persons, comprehensive to all acts, non-arbitrary in its premises, and logically consistent. If one presents an ethic which fits these criteria, then the universal ethic exists.
2. The premises of natural moral law are the biological independence of individual thinking and feeling, the moral equality of persons, and the existence of a personal ethic in each person’s mind. The first two were proposed by John Locke in his Second Treatise of Government. The equality premise is based on the common observation that there is in human nature no inherent basis for one group of persons to be superior masters over a second, inferior, group.
3. The derivation of natural moral law, as expressed by the universal ethic, provides rules for the three moral values (good, evil, and neutral). Good acts are welcomed benefits. Evil acts coercively harm others, as invasions, in contrast to merely offensive acts that depend only on the beliefs and values of those affected. All other acts are morally neutral.
Those who reject moral realism ask about the fact-value problem, the proposition that one cannot derive a moral value from any observed fact. The answer is that the universal ethic does not create any values. The values are held by individuals, in accordance with the third premise, the existence of personal ethics. The universal ethic is a production function which inputs individual moral values (good, evil, and neutral) and transforms them into universal ethic moral values. For example, if a theft takes place, the individual moral value is that it is evil, and since the theft is an invasion, a coercive harm, this individual value becomes a universal ethic value.
If, in contrast, a person observes someone who is walking naked on his property, and judges that to be evil, the universal ethic inputs that value and makes it neutral for the universal ethic, since that is an offense rather than an invasion into another’s property.
Therefore, the natural moral law does not generate values from facts, but rather, produces natural moral law values by inputting personal values and then applying its rules to output universal-ethic values.
Some skeptics reject natural-law moral realism because its premise of personal equality cannot be proven true the way that, say, the law of gravity is shown to be true. The proposition that there is in human nature no inherent master/slave relationships can be observed and inferred, but the conclusion is not apodictic, i.e. absolutely certain. However, the alternative is either supremacism, the alleged superiority of some religion or creed, or else nihilism, the absence of any transcendent morality, and either one leads to war.
The purpose of the universal ethic is the moral basis of proper governance, and since to my knowledge, nobody has come up with a superior moral idea, the ontology is good enough for the practical purpose of providing social peace and harmony with nature.