About and against ethical subjectivism:

David Hume is perhaps the best known philosophical advocate of subjectivism. According to his view, also known as emotivism or “Yea – booism”, expressions like “Murder is wrong” don’t assert anything about the way the world is (like, say, “the sky is blue” does). Rather express our ethical sentiments and should be understood as exclamations (expressions like “yea, go team go”). Exclamations do not have truth values. Likewise, Hume’s view is that ethical expressions do not have truth values. Hume is lead to this view by his rather strict empiricism. Empiricism is a view about justification in epistemology (the theory of knowledge). Empiricism holds that all of our knowledge is ultimately justified by our sense experience. Ethical views are not justified by sensory evidence the way that scientific knowledge is. Given this the empiricist infers that we lack knowledge of ethical facts. I won’t go into to reasons that lead Hume to hold that there are no ethical facts. But do notice that this is a further view that requires further argument. It’s a view about what sorts of truths there are, not a view about the limits of human knowledge of those truths.

Note that subjectivism is not the view that anything goes. That anything you like is morally OK is an ethical claim and Hume denies the existence of any truths that such claims might be used to express. Lots of people seem worried that if there are no ethical truths, people will be as vicious as they like and the moral fabric of society will crumble. Hume did not share this concern because he thought the essential moral sentiments were universally shared by all people. He certainly had good moral sentiments. He had lots of friends and was active in politics and political philosophy. Among lots of other important essays, he wrote a rather timely critique of public borrowing.

Immanual Kant’s realist ethical theory is developed in response to Hume’s subjectivism. Part of Kant’s reply to Hume involves rejecting his strict empiricist epistemology.


Against subjectivism:
Here I want to discuss just one consideration that I think speaks for of a realist view of ethics over the subjectivist view. We seem to reason about ethics quite a lot. We don’t just express ethical sentiments, but we incorporate ethical expressions into complicated strings of expressions that look for all the world like arguments. People who think abortion is wrong don’t just say “abortion is wrong” but, sometimes at least, they also say things like “abortion is wrong because the fetus is a person and it's wrong to kill a person." It certainly seems like what is offered here is an argument. And we commonly evaluate such expressions as if they were arguments. But if the subjectivist is right, then whatever the opponent of abortion offers with this expression, it isn’t an argument. That’s because an argument consists of a series of claims that admit of truth or falsity. In order to be a part of an argument (in order to be a premise or a conclusion) a sentence has to be a statement that makes some claim about how things are (and therefore is capable of being true or false). But the subjectivist who follows Hume in taking moral sentences like "murder is wrong" to be mere expressions of sentiment, equivalent in this case to "Boo murder", denies that such sentences make claims that admit of truth or falsity. I think this is a cogent abductive reason in favor of a realist ethical theory. At the very least, the subjectivist owes us an adequate alternative story about what we are doing in our ethical discourse if we are not offering and evaluating arguments and it is not at all clear how the subjectivist might accomplish this.