In my last post on Moore's Open Question argument I made the case that this was nothing more than a dressed up version of the Argument from Intuition. I want to expand on his argument with further objections that are sometimes used against a naturalistic reduction and end with some thoughts of the irony of moral subjectivists using this argument.
The "synonym" objection
This is the demand that the reductive definition be a synonym for "good". This is an unreasonable and unjustifiable demand. For example what is the definition of "big"? If one were to answer with "large" this would be rejected on the basis that it is a synonym and not a definition. So arguing the other way here is equally misplaced.
The "1:1 correspondence" objection
Mackie, in Inventing Right and Wrong, argued, correctly in my view, that "good" was an indetermined term - so I call it the "indeterminancy of good" argument. It might be indetermined but not necessarily more so than other relational terms such as "big", for example. One could also take a latter Wittgenstinian approach and argue that good is a term with multiple but related meanings with family resemblances. One needs to address particular meaning of "good" not a vague broad sense and so to demand a 1:1 correspondence is another unreasonable and unjustifiable demand.
Further, Mackie dealt with this by making explicit and internalising it with his reduction of good to "such as to satisfy the requiredments or interest or wants of the kind in question". The emphasized phrase "of the kind in question" captures this indeterminancy. And if one presents a specific definition which addresses a specific "kind in question" then it is an invalid ojection to use a differing meaning of good which makes reference to another kind of question not being answered in the presented definition. One can always make such a move but this is a fallacious basis to defeat a candidate definition.
The "obvious" objection
Can any successful definition of "good" be an "obvious" tautology? Well if it were truly obvious there would not be much debate would there? However is this demand useful in a hindsight usage of "obvious" - similar to, say, Huxley's usuage of "obvious" in responding to Darwin's Theory of Natural Selection - that once he had seen, it was so obvious that he was annoyed he had not thought of it first? Well even in this hindsight usage of "obvious" requires the willingness of the challenger to accept this "obviousness" yet that they are quite entitled to look for and criticise any definition even if it, once presented them, strikes them as obvious (they might be mistaken in seeing this obviousness after all) and this is the way to test the robustness of such a definition. To say that it is not obvious alone is another dubious riposte and is not sufficient to reject a definition. It might be obvious to the definer but not to the critic. As it would do not good for the definer to argue that it is obvious it also does not good for the critic to reject it because it is not obvious.
The "tautology" objection
Behind the obvious charge is the assumption that such a definition should be a tautology, although this objection can be made separately. Still is this justified? Well we are looking at providing a reductive definition, one that performs an ontological reduction in some empirical and not purely logical sense, whereas tautologies apply in the domain of logical relations. So no it is not justified.
How can moral subjectivists invoke any of Moore's naturalistic fallacies?
Moore's argument is popular with moral subjectivists which is ironic because Moore was making a case for moral objectivism, arguing for, in some sense, a modern version of Hutchinson's moral sense theory. Two names were applied to this theory, one was moral intuition where what was being intuited were objective features of the world. This theory, was unfortunately in my view, also called ethical non-naturalism which can cause confusion. A charitable interpretation is not that Moore was arguing for a supernatural based dualism, but rather he was using "natural" in a narrow sense - more akin to physicalism or materialism one might say - and arguing for a natural dualism, where I am here using "natural" in the broad sense. To expand, that is, a broad naturalist view of the world is not isomorphic with materialism or physicalism but can cater for some form of ontological dualism or pluralism, whilst still rejecting any form of supernaturalism. Using this distinction over naturalism for a charitable interpretation, we can then say that Moore was arguing for at least a natural ontological dualism - where the moral features and values of the world are still natural but not reducible to material or physical features. The moral sense and resulting intuitions were the means for us to detect these ontological distinct and objective features of the natural world. This works with all three versions of his naturalistic fallacy - basicness, non-materialness (used here as a better term for the distinction I noted in the previous post as "non-naturalness") and specialness - where methodological reduction fails because, we can say for our purposes here, it requires some form of ontological monism.
Here comes a potential problem for moral subjectivists. How can they argue that a reductive naturalist is committing the naturalistic fallacy - in any of Moore's senses - without also committing themselves to the supposition that such values objectively exist in some basic, natural but non-material or otherwise just special category immune to methodological reduction, that is commit themselves without contradicting their subjectivism? Indeed can they invoke any version of the naturalistic fallacy without contradicting there position?