I think I first heard this story while listening to a debate between Michael Horner and Henry Morgentaler, but since then I’ve seen it or heard it repeated many other times. The story is supposed to illustrate that even people who claim to be moral relativists really do believe that objective moral values exist. Here is how Victor Reppert puts it.
Lewis’s first argument is the argument from implied practice. People are, at best, inconsistent moral subjectivists. He writes:
[quotation of C.S. Lewis snipped]
1. If ethics is subjective, then we should expect people to recognize that actions which they are inclined to think of as “wrong” are only wrong from their point of view.
2. But invariably, people view wrongs against themselves as actions that are really wrong.
3. Therefore moral values are objective and not subjective.
Some examples may help:
1) A student once wrote a paper for a professor defending moral subjectivism. He made extensive use of anthopological and sociological evidence and the paper was well-written. He put the paper in a blue folder and gave it to the professor. The professor returned it with an “F” and said “I do not like blue folders.” The student, of course protested, pointing out all the effort that went into the paper. the teacher replied “Your paper argues that moral values are subjective, that they are a matter of preference?” Yes, replied the student. Well, the grade is an “F” I do not like blue folders. Of course the student could say “But that’s not fair,” but to do so would, of course, compromise his subjectivist principles.
I’ve never underst0od why this story (and others like it) are supposed to defend premise (2). In fact, it seems to me that this story begs the question against subjectivism. To say that a proposition, such as “Murder is morally wrong,” is objective to say that the truth of the proposition is independent of the subjective states (beliefs, attitudes, desires, intentions, goals, etc.) of persons. To say that a proposition is subjective is to say that the truth of the proposition is determined by the subjective states of one or more persons.
Suppose you to go an ice cream store with a friend. You order chocolate and she orders vanilla. Your friend frowns and says, “Oooooh! Chocolate ice cream is gross! Yuk!” You start licking your lips and reply, “Mmmmm.. Chocolate is the best!” I think everyone would agree that the “yumminess” of ice cream is purely subjective. Although it might seem that you and your friend have a disagreement about chocolate, you actually don’t. Since both of you are subjectivists about ice cream, each speaker is simply expressing their preferences about ice cream flavors. When your friend says, “Chocolate ice cream is gross,” she isn’t saying, “There exists a neo-Platonic realm of abstract objects which include the ‘Form of the Best Ice Cream,’ and that Form is vanilla ice cream.” No! She’s simply saying, “I don’t like chocolate ice cream.” The only way the two of you could have a disagreement would for you to argue something like, “No, you like Chocolate,” or for your friend to argue, “No, you hate Chocolate.”
Similarly, in the blue folder story, if the student says, “But that’s not fair,” that doesn’t mean the student is appealing to an objective moral standard. The student, as a moral subjectivist, could simply be saying, “I don’t like unfairness.” Of course, that would simply invite the reply, “So what? I don’t.” A much more charitable interpretation is this: when the student says, “But that’s not fair,” the student is appealing to the professor’s belief in the moral wrongness of unfairness. If the professor believes it is morally wrong to be unfair, then the moral subjectivist student can consistently appeal to the professor’s belief in the wrongness of unfairness without presupposing an objective moral standard. In fact, this would be the case even if both the student and the professor were moral subjectivists!