The paradox of infallibility: It has been generally supposed that certain self-ascriptions, such as "I am in pain", are infallible. This seems right. However, it is clear enough that the self-ascriptive thought is not identical to the state ascribed: the pain isn't the same as the thought about it. This means that these are "distinct existences", in the Humean sense. But if they are distinct existences, they can be conceived apart, which implies that they are contingently connected. So there must be worlds in which the ascription occurs without the state ascribed--which would make the ascription false. So the ascription is fallible. How then can we maintain infallibility while accepting that distinct existences are contingently connected? This is the puzzle of infallibility. How can the metaphysics (distinct existences) be made to fit with the epistemology (infallibility)?The theorem "2+2=4" seems distinct enough from, i.e. not identical to, each of the axioms of arithmetic and the derivation rules of propositional calculus. But of course "2+2=4" is a theorem in *all* possible worlds where the axioms are true and the derivation rules sound; one could, I think, legitimately say that 2+2=4 is both distinct and infallibly a theorem of arithmetic. It would thus appear that there is an enthymeme in the argument which is, if not definitely false, then at least poorly-defined.
Do we need ontological infallibility, though, especially when infallibility is explicitly discussed in an epistemic sense? Could we not simply look at at epistemic "infallibility" as simply the impossibility of knowing one was wrong? What's the difference, in pragmatic, practical terms, between a belief which is actually true and a belief which is logically impossible to determine is false? To even differentiate these sorts of beliefs, would we not need to gratuitously introduce ontological elements which have no explanatory power?
I must also dissent from affirming that "phantom" pain from a missing limb is in any sense a canonical example of a specifically false pain. It would seem that on a simple, scientific view, the experience of such pain is just as genuine as the experience of pain that results from actual stimulation of the peripheral nerves. In other words, if we use some super-duper sensor to look at people's brains, we would find brain states similar in all respects.
Indeed, just because we might hypothesize two entities: the experience of pain and the self-ascription of pain, does that mean that there is necessarily an essentialist definition of either? We might, rather, define a "pain experience" as just that sort of experience necessary to elicit the corresponding self-ascription. We might then be able to talk about pain experiences in reductive, neurological terms, but that reduction would depend on the more fundamental operational definition, and the reduction would apply at best only to typical human beings or perhaps might always be idiosyncratic.
Whence Value? Is something valuable because we value it or do we recognize value in something that it has independently of being valued? (Compare: is something good because the gods say it's good or is goodness something that the gods in their wisdom recognize?) One way to answer this question is to ask if there can be mistakes of value--this suggesting that value is logically independent of valuing. Consider a tribe that eats both carrots and broccoli. Both nourish them and taste equally good. They have value. However, the religion of the tribe decrees (for no good reason) that carrots are the godlier vegetable and dedicates a good deal of reverence and ritual to the act of carrot eating. They regard carrots as of far more value than broccoli. Aren't they simply wrong about this? Carrots and broccoli have equal value, in fact ("objectively"), but they are mistaken about this; they have been misled by their religious ideology. (Compare the value placed on chastity in our religious tradition.) Thus, value is not determined by valuing.I think the McGinn's argument fails on a number of fundamental points.
Let us assume arguendo that valuing really does not determine value. In this case, however, we must admit not only "latent" value (value that is not valued) but also "hallucinatory" value (specifically the "wrong" valuing that McGinn ascribes to the tribe's differentiation between carrots and broccoli). Since we have to grant both, there is no mutually determinable way for McGinn and the tribe to resolve their difference: McGinn might be correct that the tribe is engaging in "hallucinatory" value, but it is equally plausible that the tribe might be correct: they have discovered a "latent" value to which McGinn is blind. Separating value from valuing thus does not epistemically differ from conflating value and valuing: a difference which makes no difference is no difference.
The notion that the experience of eating carrots is identical (and thus deserves the same value) as the experience of eating broccoli depends on the same sort of essentialist definition of experience I denied in my comment to The paradox of infallibility above. If we admit to only an operational definition of experience, then we can infer identity of experience only from identity of reportage. In this case, since the tribe makes different reports about eating the different vegetables, we have no basis in evidence for concluding that the experiences are identical. And again, we might find a neurologically reductive explanation, but that reductive explanation, being dependent on the operational definition, would therefore not be an essential definition.
The Constitution of Value: It is often held that something has value only in virtue of being valued by some evaluative being: value is conferred on something by the attitude of valuing. This is supposed to be true even of pleasure. But is the act of valuing itself something that has value? If not, it is hard to see how it could confer value on other things. But if it does have value, then it must do so in virtue of some further act of valuing. Then that valuing in turn must either lack value or have it in virtue of a further act of valuing. An infinite regress results from the latter horn of the dilemma. Therefore, not all value can be had in virtue of acts or attitudes of valuing. Pleasure, for example, is valuable in itself, irrespective of whether anyone regards it as valuable.I think the first sentence of the post, "It is often held that something has value only in virtue of being valued by some evaluative being: value is conferred on something by the attitude of valuing," is so deeply idiomatic and metaphorical that it cannot serve as a basis for any deep philosophical investigation. Under coherent subjectivist views of valuation, things don't have value. Full stop. There are only evaluative beings making evaluations. Value is not ever "conferred" in any literal sense.
That we speak of things or states having value is simply an idiomatic metaphor. We employ the metaphor because language has to be initially socially constructed by appeal to the physical, extrinsic properties of real objects, and is therefore biased towards those sorts of descriptions.