In his book Principia Ethica G.E. Moore presented the idea that moral terms such as 'Good' are indefinable.

To give an example of another indefinable concept, he uses 'yellow'. The perception of the color yellow produces a mental state which he claims cannot be defined to a person who has never experienced it. The same goes, he claims, for concepts like Good, Right, and Ought.

His main defense of this is that the sentence "I know it's Good, but does it produce pleasure?" makes perfect sense, while (For example) "I know he's a bachelor, but is he an unmarried adult male?" does not. Surely, if we had the correct definition, it would be senseless for us to say, "I know it's good, but is it {Correct Definition}?"

It seems that no matter what we put into the second half of that question, the sentence will make sense.
"I know it's good, but does is it in accordance with nature?"
"I know it's good, but does it produce positive utility?"
"I know it's good, but is it soy?"
None of these sound like pointless questions, at least not in the way "I know it's a square, but does it have four equal sides?" does. *

This idea that good can only be understood as good was quite strong for a good long while. Moore published Principia Ethica in 1903. I don't know when the naturalistic fallacy was overturned, but in it's time it was compared to Hume's famous "You can't get Ought from Is" argument (Hume's Maxim).

The Counter Argument

Moore seems to be confusing meaning and reference. Meaning is what you mean, while reference is what the word picks out. (I know that didn't help. Next up, a demonstration!)

An oft-used example to demonstrate the difference is the morning star and the evening star, both of which are Venus, seen at different times.

When I say 'evening star' and 'morning star', I mean two different things. (By evening star, I mean that bright star I see in evening, and by morning star I mean that bright star I see in the morning.) But they both refer to Venus. (When I talk about the morning star, I am referring to Venus, even if I don't mean to).

So when I say, "I know it's the morning star, but is it that bright star I see in the morning?", it makes no sense -- but when you say, "I know it's the morning star, but is it the evening star?", this is a useful and relevant astronomical question.

Statements like "I know it's good, but does it produce pleasure?" make sense because, even while they may refer to the same thing, they may mean different things. Statements like "I know it's a square, but does it have four equal sides?" both refer to and mean the same thing.

* Confused? If so, here is some more explanation. If not, skip this.

If you know what a square is, and you know what 'four equal sides' means, then you know that if it is a square, then it does indeed have four equal sides. When asking "I know it's a square, but does it have four equal sides?", you will not be getting any useful information when you get the answer.

Moore is saying that if you were to have a good definition of the word 'good', then you will be able to formulate a question of the form "I know it's good, but is it X?" that is redundant. He also thinks that there is no question such that it starts out "I know it's good, but is it....", and such that that the second part is redundant. People do indeed come up with complex counter examples to show that things that 'make you happy', 'produces the most overall utility', 'is in accordance with nature', etc., etc. are not always definitely good.

Cletus the Foetus is defending Hume's 'you can't get ought from is' (Hume's Law), and it seems that the way he is doing it is compatible with what Moore is saying. I'm still trying to figure out if it can be considered the same thing. But it looks like Cletus the Foetus knows what he is doing, and is quite good at it.

Moore did not use induction and tautologies to explain his views, but they might have been stronger if he had.

The naturalistic fallacy is an abuse of induction and categorisation. It breaks down, because you can't get ought from is, for the following reasons.

Let's take a look at the traditional occurence of the naturalistic fallacy.

1: Human nature is such that people do not kill their parents. (This is induced from a certain number of encounters with people.)

2: Lizzie Borden was a person. (This is observed.)

Therefore: Lizzie Borden should not kill her parents. (This is where the naturalistic fallacy is committed. We'll look at this more later.)

3: Lizzie Borden did kill her parents. (Again, this is observed.)

Therefore: Lizzie Borden has defied the moral order and compromised her own existence as a human being.

Not that I'd defend Lizzie Borden or anything, but this argument is fallacious, and I'll show you why. Postulate #1 is induced. Let's take a look at another induction, this time a scientific one.

1: All animals which fly lay eggs. (This is induced by studying a certain number of animals which fly.)

2: Pigeons are animals which fly. (This is observed.)

Therefore: Pigeons must lay eggs.

This is an entirely valid use of induction. The conclusion is as true as the induction, and when we see that pigeons really do lay eggs, we can rest even more secure in our supposition that everything that flies lays eggs. But let's take a look at a situation where induction breaks down.

1: All animals which fly lay eggs. (Again, induced.)

2: Bats are animals which fly. (This is an observation.)

Therefore: Bats must lay eggs. (!!!)

3: Bats, in fact, don't lay eggs. (This is observed.)

Now, in order to avoid contradiction, we have two options. We have to ditch one of our premises; either not all animals which fly lay eggs, or bats aren't animals which fly, or bats actually do lay eggs. But #2 and #3 are observations of bats themselves; #1 is an induction based on observing a number of flying animals, none of which were bats -- but the essential feature of the category is not the egg-laying, but the flying. The induction is therefore provisional; we can ditch it with a clean conscience.

This is how induction is supposed to work. But let's get back to the fallacy, and use the bats as an example again.

1: All animals which fly lay eggs. (Induced.)

2: Bats are animals which fly. (Observed.)

Therefore: Bats are morally obliged to lay eggs. (Here's the fallacy. I think you see where this is going.)

3: Bats don't lay eggs. (Observed.)

Therefore: Bats are depraved little heathens who defy the natural order.

This is obviously pretty silly. Bats cannot be held morally accountable for not laying eggs; they can't be held accountable for not wanting to lay eggs; and we couldn't hold them accountable if we offered to genetically engineer them to lay eggs and they refused.

But by the same token, we can't hold Lizzie Borden morally accountable if she kills her parents. We can say that she's not a person – but she was obviously a "person," a sentient member of the species homo sapiens, citizen of the United States of America, and what-have-you. We could say that she didn't really kill her parents, and that they died of natural causes – if we wanted to ignore history.

The only thing we can say is that the concept of "human nature" touted in the first premise of the argument, is incomplete. Just as "some animals which fly don't lay eggs," so too "some human beings kill their parents." And you can't determine that they shouldn't based on induction, or observation of phenomena. You would have to assert it as a tautology – if at all.

And that, in a bat's eggshell, is the naturalistic fallacy.

Tem42: The naturalistic fallacy hasn't been "overturned" because it actually is a logical fallacy. G.E. Moore was not confusing reference with meaning. That's the accusation he levies against those who commit this fallacy -- hence his insistence on the two different types of questions about definitions, ones which "make sense" when you turn them around, and ones which don't. This distinction mirrors the difference between induction and tautology, and also of what you call "reference" and "meaning," respectively.

There are two basic ways of making a categorical statement: tautology and induction.

A tautology is a definition that names a certain set of traits. For example, a "square" is a closed geometric figure consisting of four equal sides. A "bachelor" is an unmarried adult male -- so "All bachelors are unmarried adult males." To accept one term is to accept the other; so to ask, "I know it's a square, but does it have four equal sides?" doesn't "make sense" -- it's obvious, because it's tautological.

An induction, however, is different. Given a definition, you go out into the field and observe a number of different instances of that definition. In the case of bachelors, one might induce that "All bachelors eat Kraft Dinner." This is a completely different sort of statement than "All bacehlors are unmarried adult males." It also makes perfect sense to ask, "I know he's a bachelor, but does he eat Kraft Dinner?"

When making inductions, there is a fallacy that one is to avoid which is called "Slothful Induction." Slothful induction, which is closely related to the naturalistic fallacy, is when you make an induction, and then insist that it is correct and needs no further revision. In the sorts of cases to which the naturalistic fallacy applies, these inductions are about "good" and "evil" and "human nature."

The naturalistic fallacy, in essence, consists of:

1: Making an induction.

2: Forgetting that, as an induction, it is provisional, and mistaking it for a tautology. (Also known as "sloppy thinking.")

3: When the sample or observed phenomenon differs from expectations based on the induction, you blame the sample rather than inductive error. (Also known as "counterproductive pride.")

So when people do things that you have decided are "against human nature," it's their fault for being depraved, not your fault for not knowing what human nature really is or leaving your mind open to new evidence.

Where Moore and I disagree is on whether a tautology of "the good" is possible or useful. He says it is; I say it ain't. In any event, he has accurately outlined a very real inductive fallacy which is committed by almost every single moral philosopher since Christianity came to Europe.