Ethical non-naturalism is the view that ethical sentences express propositions, and that they cannot be reduced to nonethical sentences.
So the way that we're defining these views, naturalism and non-naturalism are both kinds of cognitivism -- that is, both of them share the view that ethical sentences express propositions. What they disagree about is whether ethical sentences can be reduced to nonethical sentences. Non-naturalism says they can't. As that British philosopher of common sense, G. E. Moore, said, goodness is a simple, undefinable, non-natural property.
To call it "non-natural" doesn't mean that goodness is somehow supernatural or ghostly or divine or anything like that. All that it means to say that goodness is non-natural is to say that it can't be reduced to natural properties like human needs, wants, pleasures, and so forth.
Or to say the same thing, goodness can't be defined in terms of anything else. So Moore thought that goodness is indefinable. Now, does that mean that he thought that talk of goodness of nonsense? Definitely not: talk of goodness is quite meaningful. It's just that you can't formulate what this meaning is in a definition. You can't say, for example, "goodness" means "pleasure." Moore said you couldn't give any definition like that at all.
Still, you might wonder, how is it possible that a word could be meaningful, and yet indefinable? Well, let me give you an example of another word that is definitely meaningful, but you couldn't give any plausible definition of it: "thing." I mean "thing" in its broadest sense. How could you define this? Something is a thing if, and only if, ... what? How could you finish this definition? Or how about the word "whole" as in "whole and part." Something is a whole if, and only if, it ... what, has parts? OK, but then define "part" for me, and do that without referring to wholes. You can define wholes in terms of parts, or parts in terms of wholes, but as far as I can tell, you have to take either "whole" or "part," one of those words, as primitive, undefinable, or basic. Here's another example: the word "and" and "not." These are extremely important words in logic; but all logicians admit that you have to start out with some basic, undefined concepts in logic, and in fact "and" and "not" are often two of their choices for undefined terms. Then they proceed to define other terms in logic using "and" and "not." And I'll bet you can think of all sorts of examples of primitive, undefinable terms from mathematics and geometry -- such as "point," as in "point on a line." Anyway, you get the idea.
So Moore's claim, which is the central claim of the non-naturalist, is that "good" is indefinable. And if that's the case, then the meaning of sentences containing word "good" can't be explained entirely in terms of sentences not containing the word "good." You can't substitute talk of pleasure, or needs, or anything like that for talk of good. Once you are talking about goodness (or badness, for that matter), you're talking about a subject that is just as fundamental as talk of things, of wholes and parts, of "and" and "not," and of points on lines. Just as those things are simple and indefinable, so goodness is simple and indefinable. So said Moore. That's the basic contention of non-naturalism.
OK, so why think that non-naturalism is true? Why think that "good" can't be defined? Are there any arguments for that claim? There are some, or two anyway, that we can look at.
The first argument for non-naturalism is really very simple. In fact, maybe we shouldn't call it an argument; it's better to look at it as simply a way of putting certain facts into perspective; call it a "line of thought." Consider, on the one hand, properties like hardness, roundness, dampness, and so forth. These are all natural properties; we encounter them in the real world and we can perceive them. Consider, on the other hand, properties like being good and being right. We say that a great novel like Moby Dick is a good thing; so goodness is a property of that novel. And we say that paying back debts, and telling the truth, are generally the right things to do; so rightness is a property of certain human actions, like paying off your debts, and truth-telling.
But isn't it straightforwardly obvious that these are two really quite different kinds of properties? Those natural properties, like hardness and roundness, can be perceived and encountered in the real world. On the other hand, goodness and rightness -- well, where are they? Can you see the goodness of a novel? Can you touch rightness? Can you use scientific instruments to measure morality? Of course not. So it seems simply obvious -- or so goes this line of thinking, which we won't dignify with the name "argument" -- that goodness and rightness aren't natural properties. And if that's the case, they can't be defined in terms of any natural properties; if they could be, then they would be, ultimately, natural properties themselves. Moore actually went so far as to say that it's a fallacy to think that goodness is a natural property: he called this the naturalistic fallacy. But really all that amounts to is calling naturalism a fallacy -- which doesn't prove anything. I could just as easily say that non-naturalism is a fallacy, and say that Moore committed the non-naturalistic fallacy!
Anyway, I think a lot of people find this line of thinking fairly plausible. There does seem to be something inherently fallacious about thinking of goodness as a natural property.
But this raises a rather difficult question. See if you can think of any answer to it yourself. Suppose for a moment that Moore is right, and that goodness is an indefinable, non-natural property; you can't bump into it, or see it, but you do know when novels, and foods, and states of mind, are good. But if goodness isn't a natural property, then how do you know this? You should be able to tell me what sort of question that is -- a question that asks, "How do you know that something is good?" It's an epistemological question. But in particular we're talking about knowledge of moral facts. There's a branch of epistemology, or of ethics, or both, called moral epistemology which studies how we know moral facts, and how moral beliefs are justified.
If Moore says that goodness is a non-natural property, then how does he know that anything is good? It's evidently not by any ordinary, natural process. Think about that. If you could know that cake is good by some natural process (say, just by eating it and having a pleasant taste sensation), then you could identify the goodness of the cake as some natural property that that natural process detected. For example, the cake gives you pleasure; that's how you know it's good; so you can say that the cake's goodness is just the same as, and is reducible to, the fact that it can give you pleasure. That's the idea. That's how you'd know that the cake is good, if you thought that goodness might be a natural property. But if you're Moore, and you think that goodness isn't a natural property, then how do you know that anything is good? How do you distinguish the good things from the bad?
One answer that has been fairly common among British philosophers, although not so much anymore, is to say that we have a special faculty, a faculty of moral intuition. And this faculty tells us what is good and bad, right and wrong. The view that there is such a faculty is called moral intuitionism. So we taste the cake and this faculty kicks into gear and tells us that it is good. That's not such a great example, though, because even the non-naturalist might want to allow that, when we say that cake is good, we just mean that we like it. But what about a good person, or a right action? If we see a good person, or a right action, and our faculty of moral intuition is sufficiently developed and unimpaired, then, the moral intuitionists say, we can simply intuit that the person is good, or that the action is right.
Now, don't ask me what "moral intuition" means. All I know is that it is supposed to be a mental process that is different from other, more familiar faculties like sense-perception, and that moral judgments are its outputs. So when you judge something to be good, or some action to be right, then you're using your faculty of moral intuition. And that faculty is attuned to those non-natural properties. Perhaps the best ordinary notion we have, that approximates the notion of a faculty of moral intuition, would be conscience. If I get a pang of conscience after I do something I know is wrong, my faculty of moral intuition has kicked in and is being directed at me.
We could go on and talk about moral intuitionism for a long time, because there are, believe it or not, lots of different varieties to the theory. But we can't afford the time. I will just say this about it -- that we should see whether or not we can explain how we might come to know moral facts without talking about some mysterious faculty of moral intuition.
So let's look at the second argument for non-naturalism. This is called the open question argument, and was introduced and made famous by Moore. This argument is actually one of the things that Moore is quite famous for. Which is unfortunate, because later on in his life, some years after he published the argument, he said that it was no good!
Even if the argument is no good, it's instructive to look at it. If you take a class in ethical theory, you'll probably study it again in more depth. But actually, the argument is pretty simple. It goes like this.
Suppose I want to give a definition of "good." So I say that "good" means "pleasure-causing." In other words, according to my definition, if something is good, that means it causes pleasure; and if it causes pleasure, then it is, by definition, good. But Moore complained that we could always ask, "But are pleasure-causing things good?" And the point is that that would always be an open question. This means that it's not just a foregone conclusion that, indeed, pleasure causing things are good. It's an open question, a perfectly legitimate question that someone who understands the English very well might ask: Is everything that causes pleasure good?
Moore then went on to say that you could criticize any definition of goodness like that. To take another example: I could say that "good" means "desirable." So anything that's desirable is good, and whatever is good is desirable. Moore says that we can ask a question here -- what would his question be? Well, it would be this: "Is everything that is desirable good?" And Moore would observe that this is an open question. The answer isn't obvious to someone who understands the English language.
So here's the formula that you can use to generate Moore's question. If someone says "good" means X, then you reply by asking: But is X actually good? And then you observe that this is an open question. The answer is never obviously "Yes." And yet we're all competent speakers of the English language; we all know what "good" means. So if we did come across the correct definition of "good," then, the implication is, we'd be able to recognize it. But we can never just automatically recognize any definition of "good" as the definition of "good." If I tell you that "good" means X, it's always an open question, as far as ordinary speakers of the language are concerned, whether X is good. And therefore, Moore concluded, the word "good" can't be defined. It's indefinable. If it were definable, then a question of the definition in the form of "Is X good" would not be an open question. But questions of that form are always open questions. So "good" cannot be defined.
That's the open question argument. Now, you might find at least one part of it puzzling -- a part where you might have wanted to stop me and say, "How's that again? Why does Moore say that?" I mean the following step, from (1) to (2):
(1) Moore's question, "Is X good?" is always an open question to any English speaker; that is, no English speaker would be able to recognize "good" means X as obviously the correct definition.
(2) "Good" cannot be defined.
What I want to know is: How is (2) supposed to follow from (1)? Can't we admit that (1) is correct, and at the same time claim that (2) is false? I mean, why couldn't we? Consider what that would amount to. It's the following conjunction of claims: no one can recognize that any definition of "good" is correct, but "good" is still definable. Honestly why can't we say both things at the same time?
Look at it like this. Moore seems to assume that "good" can be defined only if competent English speakers would recognize the correct definition when they saw it -- and in that case, the question, "Is X good?" would be answered, "Obviously yes, discussion closed." That's how Moore viewed it. But I don't think that's correct. It seems entirely possible to me that "good" might have a definition which ordinary English speakers wouldn't recognize when they saw it at first. You'd have to argue that the definition was correct.
Compare the situation to other attempts at definition in philosophy -- like the case with "knowledge." We all have a pretty good idea of what the English word "knowledge" means. But does that mean that if we see the correct definition of "knowledge," we'll immediately recognize that it's the correct definition? Surely not.
So here's the point: there are a lot of deep concepts that are studied in philosophy, like goodness and knowledge and consciousness and so on. We all can recognize instances of these things. We will all recognize perfectly well that motherhood is good, that we know that 2+2=4, and that we are all conscious right now. But that doesn't mean that we will immediately recognize the correct account of the meaning of "good," "know," and "conscious."
So back to the open question argument. Moore says that for any definition of goodness, where we say "good" means X, you can always ask "Is X actually good?" and that will be an open question. But my reply -- which is not just my reply but a fairly common reply to Moore -- is to say that that proves nothing. Even if it's an open question to ask, "Is X actually good?" it doesn't follow from that that X is not the definition of "good." It might be, for all we know. We won't necessarily recognize a truly enlightening theory of goodness when we see it. That's a perhaps unfortunate fact, but I think it's true.