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2009-06-08
Rationalist Infallibilism

I've got a strictly sociological question about an epistemological doctrine: rationalist infallibilism. Rationalist infallibilism, defined somewhat tendentiously,holds that a relatively wide range of (i) analytic and (ii) synthetic a priori propositions can be infallibly justified or absolutely warranted. Here I'll define absolute warrant as a proposition that is warranted to such a degree that entails its truth and precludes its falsefood.

Are there any current  proponents of rationalist infallibilism who have made sustained attempts to defend this position in the literature? I can think of a few philosophers who have defended  either thesis (i) (e.g., Putnam) or (ii) (e.g., Burge, Lewis, Parent, Bealer), but none who defend both these theses. Are there any prominent or semi-prominent philosophers who still defend both these theses and can thereby be described as rationalist infallibilists (as I describe the position)? Or is rationalist infallibilism a completely dead position? 


2009-06-15
Rationalist Infallibilism
Reply to Glen Hoffmann
Would the Frank Jackson of 'From Metaphysics to Ethics' be a candidate? 

2009-06-15
Rationalist Infallibilism
Reply to Glen Hoffmann
There is so much work going on in this and other branches of philosophy that no general answer is possible except to say that rationalist infallibilism is out of fashion, has been at least since Carnap and Reichenbach, as far as I know.  My view is that on very few issues such knowledge is possible--e. g., in the area of metaphysics, regarding first principles such as the law of identity.  But any of the substantive fields do not afford such knowledge since one simply cannot preclude the need to update or modify current knowledge in light of future discoveries.

2009-06-15
Rationalist Infallibilism
Reply to Glen Hoffmann
Two  points. First, Tibor is right that the position has fallen out of fashion since Carnap perhaps because after Carnap, philosophers came to believe that there is synthetic (metaphysical) necessity. I believe it is impossible to reconcile (non-mysterious) rational infallibilism with the view that a priori propositions pertain to real (metaphysical) necessity and that they need justification in order to be known. To reconcile the two one would need to be a Goedelian faculty-rationalist and committed to the view that one can directly perceive facts in the third realm, which is indeed mysterious. This is why most of the rationalists are fallibilists. Bealer is a good example. He thinks that a thinker has a strong modal tie to an a priori proposition, though such a tie is weaker than infallible. Fallibilism, I think, goes hand in hand with indirect access to metaphysical necessity.

This brings me to my second point, about which I am a bit hesitant. Namely, I am neither a prominent nor a semi-prominent philosopher but I recently made an attempt to defend a version of rationalist infallibilism in my dissertation. Crucially, basic a priori propositions and what follows from them need not and cannot be justified. The reason for this has something to do with the analytic nature of such propositions and the concept of justification.  Another (unorthodox) feature of the view is that according to it one has to be a Carnapian about necessity to defend both the very possibility and infallibility  of a priori knowledge.


2009-06-16
Rationalist Infallibilism
Reply to Glen Hoffmann
Thanks for the replies. Haven't read the Jackson article: I'll need to take a look. So there seems to be a consensus so far that no prominent philosophers continue to defend rationalist infallibilism (as I define it). I agree with Tibor that, contra Burge and Lewis, no substantive synthetic a priori proposition can be infallibly justified. I'm inclined to say that at best a cognitively insignificant putative ontologically necessary truth can be infallibly justified a priori, such as something exists.
 
Interesting, Ivana, that you argue that certain basic a priori propositions can be infallibly justified. If it is a basic a priori proposition, and so primitive as not to be susceptible to justification, can we still say that it is infallibly justified (i.e., justified to a degree that is truth entailing and falsity precluding)? Intuitively I would think not and in fact I'm trying to argue against this position in a paper in progress. Perhaps, Ivana, you could send me relevant chapters of your thesis.

2009-06-16
Rationalist Infallibilism
Reply to Glen Hoffmann
Glen, a small point:  I would not use the term 'infallibly justified' since I argue that the notion of a priori justification when applied to a priori propositions (basic or nonbasic)--that is, in the context of a prioir knowledge--does not make good sense. (I spend I lot of time arguing for this because it is absolutely not fashionable to think this).  Anyhow, we, at least, seem to agree about the basic a priori propositions. I would be very interested in seeing a draft of your paper if you are inclined to share. I shall send you the chapters you asked for. Sorry that the link I posted earlier is broken.



2009-06-16
Rationalist Infallibilism
Reply to Glen Hoffmann
I think that last point (Hoffmann post) is right too. So I'd be committed to: basic-ness has the force of primitive-ness; if not not. Jackson, by the way, a little like a number of other people, reduces the significance of some related intuitive dependencies, and then explicates, as he would say 'meaning relations' in terms of possibilities. He then has dividers among those possibilities, allowing for metaphysical and conceptual truths (roughly). However, the philosopher (very roughly) gets to push some buttons marked A or C intension in order to have some of these possibilities later collide -- that is, according to suitably informed reports. One can take the thesis as remarking inevitability (if not quite infallibility) of the colliding procedure, according to reports. So it's a kind of mean spirited Quinean take on infallibility and justification by way of involved essentialism that actually makes room for the infallibly justified (in that mean sense which may not interest you).

2009-06-17
Rationalist Infallibilism
Reply to Glen Hoffmann
I think I'm fairly close to being a rationalist infallibilist as defined.  At least, I hold that there is such a thing as "conclusive a priori justification", justification that conclusively rules out the falsity of the justified proposition (see "The Foundations of Two-Dimensional Semantics" among other places).  And I think that conclusive a priori justification is possible in principle for many truths, including logical and mathematical truths, many traditional analytic truths, and some synthetic apriori truths as well (I also think there can be conclusive a posteriori justification, e.g. for the proposition that I am conscious).  I don't explicitly gloss this notion the way that infallible justification is glossed above.  But I'm not opposed to doing so, apart from one worry.  The worry is that I think that in principle any justification may be subject to "metacognitive skepticism", doubts arising from the possibility that one's reasoning abilities have been affected.  E.g. I think that no-one can conclusively rule out that they have been given an anti-mathematics drug (one that makes their mathematical reasoning unreliable), and it's arguable that if one can't do this, one also can't be conclusively justified in believing any mathematical truth (see David Christensen's "Does Murphy's Law Apply in Epistemology" for a nice argument for a thesis of this sort).  To handle this worry, in some unpublished work I define "conclusive a priori justification" to allow compatibility with skeptical doubts of this sort.  But I suppose that this means that strictly speaking I may not accept rationalist infallibilism as defined after all, but merely a close cousin.  I suspect that something similar may go for Frank Jackson.

2009-06-19
Rationalist Infallibilism
Reply to Glen Hoffmann
Okay, so it seems David Chalmers (and perhaps Frank Jackson) defend a form of rationalist infallibilism according to which at least certain analytic propositions can be conclusively justified a priori in that we can rule out their falsity. My concern with this and similar kinds of positions is precisely the one David Chalmers raises: meta-cognitive skepticism. If it is possible that an evil demon is deceiving us that 2+3=5 or that we have been given a 'anti-math' pill that makes us believe this proposition, wouldn't these skeptical hypotheses be falsifying propositions for 2+3=5? And if so, wouldn't this rule out any rationalist infallibilism according to which certain analytic propositions are warranted in such a way that is either truth entailing, falsity precluding, or both? I think we can resist this conclusion only if we can resist the logical/metaphysical possibility of the radical skeptical hypotheses; and I'm not sure how easy this would be to do. This is exactly what I argue in my recent paper 'Two Kinds of A Priori Infallibility' (I'll provide a link in the next few days).

Now perhaps we shouldn't be too worried even if we can't  have analytic infallibility (in the form of absolute warrant): analytic propositions that are warranted in such a way that is truth entailing and falsity precluding (or at least one of these). If it is only meta-cognitive skeptical hypotheses that are potential falsifiers for the propositions in question, we will still have a pretty strong form of analytic justification. But I would hesitate to call this analytic infallibility, certitude or even conclusive justification insofar as it is not a form of justification that renders the probability of a proposition 1 (i.e., that entails its truth and precludes its falsity).

2009-06-22
Rationalist Infallibilism
Reply to Glen Hoffmann
What are we taking 'infallible' to mean? It sounds at times like it's sufficient for infallible justification for p that that which provides the justification for p entails p. But this is not a very strong view -- it's certainly not ruled out by the sorts of meta-cognitive skeptical scenarios mentioned. If you think, for example, as Timothy Williamson does, that known propositions provide justification for propositions they probabilify, then you can happily believe in infallible justification about all kinds of stuff -- the analytic, the synthetic, and the deeply contingent, straightforwardly empirical. My belief that it's warm is based on the fact that it's warm; it's therefore infallibly justified in the sense that the basis entails the target proposition.

2009-06-22
Rationalist Infallibilism
Reply to Glen Hoffmann

"we shouldn't be too worried even if we can't have analytic infallibility". I think you are quite right. We shouldn't worry too much about the fact that we are limited in this way. However, analytic infallibility could still be a viable notion for reasoners who are not limited as we are. Specifically, it might be a useful notion for an ideal reasoner. This seems to suggest that rationalist infallibilism could still be true, i.e. that a "wide range of (i) analytic and (ii) synthetic a priori propositions can be infallibly justified or absolutely warranted", even though we are too limited in our reasoning capabilities to do so.

I use this strategy in my thesis "Conceivability&Possibility - The Prospects of a Reductive Account of Modality" where I argue that ideal conceivability infallibly implies metaphysical possibility.


2009-06-22
Rationalist Infallibilism
Reply to Glen Hoffmann
I think the main problem for rationalist infallibilism, when we appeal to meta-cognitive skepticism, is an internalist conception of justification. If we are internalists, so there will be always the problem of someone being math-druged. Someone that is math-druged wouldn't have reasons to belive that 2+2=4. But, anyway, 2+2=4 is justifiable externally. Even if I am math-druged, I can be convinced that 2+2=4 without a math-argument, only with a linguistic argument. So, I can think 2+2=5 (because the math-drug), but be convinced that I am wrong. And I can be convinced I am wrong because there is a external justification.
But if everybody had took the math-drug? There won't be any problems. If everybody have the same justifications to accept 2+2=5, so 2+2=5 will be part of our maths. The main problem here is that my conception makes maths analytic. 

2009-06-24
Rationalist Infallibilism
Reply to Glen Hoffmann
I think of 'infallibilism' as a thesis about putative tightness of connection between warrant and truth. With rationality producing certain connections and guaranteeing that connection; almost as though, in some cases, it were a semantic connection and one subject to caveats. Thinking back to Burge (mentioned in the first post), or Christopher Peacocke, as well, say, then there are some issues relating to preservation of contents (in judgments): level-linking; access; memory troubles etc. To which one response, I recall, was to isolate levels in terms of the realization in contents of judgments and have some actually preserve contents still subject to the standard externalist pressures. Which pressures were automatic, and automatically there realized; or as if. Actually, an interest in Jackson (as well as some others) was a connection back to this material (which I think of as slightly mid 90s). I thought of it as allowing for some separation at some level or other of what one was being considered as affirming: a difference between those contents of judgments about one's judgments on the one hand, subject to rational revision (anyway bringing in the requisite externalist considerations), and usual internalist considerations, or even just in terms of access, but which would still be subject to those externalist considerations. (Just thinking of, in Jackson, passages to do with, when for instance explicating Stalnaker, contents of a grand-daughter's beliefs; how they equate with some more sophisticated versions.) I'm sure that arguments have moved on in lots of ways and this may be simplistic, but aren't there some live issues to do with linking mechanisms, those mechanisms that connect a 'perception' about a possibility involving error or that that's a possibility even with some missed target content? So my point is perhaps a bit miniscule: rationalism taken in the sense it's been used here is/was actually a limiting feature of a kind of semantic argument focused on levels of realisation -- with some implications which would get developed later.

2009-12-17
Rationalist Infallibilism

'What are we taking 'infallible' to mean? It sounds at times like it's sufficient for infallible justification for p that that which provides the justification for p entails p. But this is not a very strong view -- it's certainly not ruled out by the sorts of meta-cognitive skeptical scenarios mentioned. ... (expand) If you think, for example, as Timothy Williamson does, that known propositions provide justification for propositions they probabilify, then you can happily believe in infallible justification about all kinds of stuff -- the analytic, the synthetic, and the deeply contingent, straightforwardly empirical. My belief that it's warm is based on the fact that it's warm; it's therefore infallibly justified in the sense that the basis entails the target proposition.'

Would it just be a crudity to ask whether there would be a collapse of distinctions -- like analytic/synthetic -- if one were to allow that a proposition was entailed by a fact in that way you mention? Wouldn't there also be something like a question of direction of fit, in giving some account of a justification of a belief? .... or one doesn't have to think of beliefs aimed at propositional justification. Justifier only, having, as it were, some status.


2009-12-22
Rationalist Infallibilism
Reply to Glen Hoffmann
Timothy and Lydia McGrew in their Internalism and Epistemology, Routledge 2007, defend (i) powerfully. They are reserved wrt synthetic a priori knowledge, though. See also Tim McGrew's Foundations of Knowledge, Lanham c. 1995, for related issues.

2009-12-30
Rationalist Infallibilism
Like Jonathan I'm not sure what "infallible" means here. First, does "one's warrant W entails p" means "(necessarily) if one has warrant W then p is true"? And do we then say that W is an infallible warrant for p iff W is a warrant for p and W entails p? If yes in both cases, we get the result that if p is a necessary truth, any warrant for p is an infallible warrant for p. So infallibilism w.r.t. necessary truths isn't a strong requirement anymore.

2009-12-31
Rationalist Infallibilism
Reply to Glen Hoffmann
Apologies for the delay. Vlastimil: Thanks for the reference. I'll have to check it out. Julian and Jonathan : I think you've got some interesting questions about the notion of infallible justification. I see the concern that, modulo its definition, infallible justification may turn out to be a weak or even trivial form of justification. To address Julian's concern directly, I don't think defining infallible justification in terms of the warrant W for a proposition P entailing P and precluding -P implies that P is a necessary truth or that all justified propositions are necessary, infallibly justified propositions. One can think of infallible justification along the following lines: W entails P iff given W the objective probability of P is 1. Now certainly some propositions have the potential to be infallibly justified in this sense yet not be necessary truths. Conceivably (for argument's sake)  the proposition that Winston Churchill sneezed 3 times on January 7, 1941 might have an objective probability of 1 which is yielded by evidence. But this is certainly not a necessary truth. In fact if we take almost any contingent proposition P we might conceive of the possibility that evidence infallibly justifies it or gives it a probability of 1 (at least if we think infallible justification is possible). The question is whether we can sensibly apply this definition of infallibility to a priori propositions. I don't see why not. I don't think any a priori propositions are infallibly justified in this sense but I don't see that it's a meaningless or insignificant question to ask whether an a priori proposition can be warranted to a degree that gives it an objective probability of 1. Perhaps, then, using entailment as the crucial notion in spelling out infallibility is not the right way to go (i.e. it's misleading at the very least).   

2009-12-31
Rationalist Infallibilism
Reply to Glen Hoffmann
Dear Glen,

My worry wasn't that only necessary truths could be infallibly justified but that (given the definition) in the case of necessary truths, any warrant for them would be infallible. (Similarly, I guess, any warrant I may have for the contingent truth that I exist will be infallible.) To put it in another way: what would you call a fallible warrant for a necessary truth? A warrant that gives it a probability of less than 1?

2010-01-01
Rationalist Infallibilism
Reply to Glen Hoffmann
Julien,

Right, so if infallibility is defined in terms of truth entailment and truth entailment is defined in terms of necessity (a warrant W entails a proposition P iff W necessarily implies P's truth), then I think you're right that all necessary (and possibly contingent) truths will be infallibly justified. So my proposal is to define infallibility in terms of the W for P rendering the probability of P 1. So yes, this would imply that a fallible proposition is one whose warrant gives it a probability of less than 1. This perhaps would require revising the initial definition of infallibility as involving warrant that is truth entailing and falsity precluding (although I need to think about this).  

2010-01-01
Rationalist Infallibilism
Reply to Glen Hoffmann
I guess I do not understand. Suppose W is some trivial math truth I know and P some highly complex math truth I do not know. Suppose further that W necessarily implies P. But then on standard accounts objective Pr(P|W) = 1. Does it mean that I am infallibly warranted in my belief in P?

2010-01-01
Rationalist Infallibilism
Reply to Glen Hoffmann
AD INFALLIBLE KNOWLEDGE AND NECESSARY TRUTHS

Once I discussed the issue briefly with Prof Tim McGrew (whose books I recommended above). I hope it's relevant here.

Sometimes infallible knowledge is explicated as this way:
S infallibly knows that p iff (S believes /or percieves/ that p) entails p. 

But this does not work for necessary propositions; otherwise, it would suffice
to believe a necessary proposition to know it.) See the discussion of Bill Vallicella at
http://maverickphilosopher.powerblogs.com/posts/1165343950.shtml .

In the ch. 2 of Internalism and Epistemology, Timothy and Lydia McGrew suggest that sometimes "we
are able to perceive the truth of an a priori claim in such a way that we could not be mistaken about it."

I wondered: does it suggests that knowledge of a priori claims consists in their infallible perceiving? If so, then the mentioned problem with necessary truths obtains. I asked about this Tim McGrew. 

He replied that "believes" and "perceives" (the latter being taken metaphorically) should be separated here. He added that there's clearly a problem moving from "S believes that P" to "S knows that P" simply because P is a necessary truth. But is there such a problem in moving from "S perceives that P" to "S knows that P," where P is a necessary truth?, he asked.

I replied that I had been just affraid that he had tacitly implied something like this:
S clearly or intellectually grasps that p iff
(S perceives that p) entails ((S perceives that p) and p).
And I added a counterexample: one can perceive very non-clearly (and
non-distinctly) a necessary proposition.

Tim replied: No, that wasn't the claim at all. He claimed I was reading "perceives" too weakly. And suggested to substitute "perceives the truth of ..."; then I should see the difference immediately. Tim concluded that this sort of intellectual perception is also, he believes, an epistemic primitive. And that Aristotle seems to have understood this; see his discussion of the status of first principles in Metaphysics IV.

2010-01-01
Rationalist Infallibilism
Reply to Glen Hoffmann
Hi Glen,

You may also want to have a look at Baron Reed's "How to think about fallibilism" (Phil Studies, 2004), which has interesting proposals.

2010-01-03
Rationalist Infallibilism
Reply to Julien Dutant
Julien, I don't know whether you (or Vlastimil) would care to pick up on this (it's a point I blurred in a previous post): In classic formulations warrant is initially connected to a belief, however, in later discussion one is frequently left with warrant applied to some statement or proposition that gave the content of that belief. Wouldn't a belief directed onto some world-state take a different bite out of probability than a statement or proposition relating one to some world-state or corresponding truth-value? This is connected with the Stalnakarian kind of consideration (itself related to Vlastimil's math point) I mentioned earlier; I'm not qualified to say how, but, is there not some consideration registering as entailment that then affects how one would give propositional equivalents, that was itself specifically, significantly entailing, or leveling?

2010-01-05
Rationalist Infallibilism
Hi Matthew,

Well I think that focusing on the probability of the belief being true vs the probability of its content proposition being true would make a difference only if we reject "content essentialism" according to which a belief necessary has the content it has. Rejecting that, we would allow a belief to have different contents across at different worlds; that's the only way in which its probability of being true can be lower than 1 if the proposition is necessary true. (NB, with contingent propositions the probability of the content proposition being true and the probability of the belief being true can go apart as much as one likes; e.g. one may believe a highly probable proposition only if it were false, in which case the probability of the belief being true is very low, while the probability of the proposition being true is very high.)

(W.r.t. to the considerations pertaining to levels you mention here and earlier: I don't feel I understand it well enough to comment on it.)

2010-01-07
Rationalist Infallibilism
Reply to Julien Dutant

Hi Julien,

Re levels: Crispin Wright, for instance, has an idea of 'basicness' sufficient to derive apriority, in the sense that it would drive relevant provisional equations; or Tyler Burge has an idea about 'critical rationality', which is an 'entitled' (rather than warranted) relation of dependency -- it is, apparently, 'the critical' relation. They make explicit either a level of characterizing as a concession, or an expressing relation -- provisional acceptance in Wright, a second-order relation in Burge (a belief about a belief) -- that's guaranteed like a content in a realization relation. Anyway, one should be conscious of movement from statements that relay some assigned content to a belief to talking about some conditions applying in a belief to seeing the independence of a potential warrant for a belief and as the sort of thing that wasn't available generally outside of some particular characterization. Of course, conceived abstractly, at that level, then one is freer to assign conditions. From the point of view of capturing beliefs as believed-in-things though -- i.e. ear-marking them to individuals -- one would end up with something like the collapsing condition upon discrete and structured propositional equivalences ..... which was why the mention of Stalnaker (in connection with Jackson), in the first place.

That's all a bit old hat I grant, I'd be interested in hearing more about whether the characterization of contingency in terms of contents, derivative forms of propositionalism etc, missed an origin of the question of warrant for beliefs as beliefs that are sources.

2010-05-20
Rationalist Infallibilism
Reply to Glen Hoffmann
HI Glen, 
You might find Evan Fales' _A Defense of the Given_ (Rowman and Littlefield 1996), epsecially Ch. 6 useful.  The book's focus is on a posteriori knowledge/justification, but I think that chapter does also touch on a priori knowledge/justification.  Fales holds that at least some foundational beliefs are epistemically infallible.

2010-05-21
Rationalist Infallibilism
Reply to Ali Hasan

Thanks Ali. I'll check that out.


2010-06-19
Rationalist Infallibilism
Reply to Glen Hoffmann
Is a demonstration from the possibility of demonstration 'infallible' in the relevant sense?

If we start from statements (rather than beliefs) can we say that a linguistic move which entails that the game is unplayable must be false, since 'this language game is unplayable' can't be a move in the game?

If this is promising, then it might turn out to be easier to go from language to intentionality, rather than vice versa, in order to deal with beliefs.

2010-06-22
Rationalist Infallibilism
Reply to Alex. Arthur
Hi Alex,

I'm not sure what exactly you have in mind by a 'demonstration from the possibility of demonstration'. As for your remarks regarding linguistic moves and language moves, I think this might involve a form of certainty or infallibility but not the type of infallibility I have in mind. For instance, Wittgenstein, in On Certainty, claims we can be certain of the truth of specific propositions, such as 2+3=5, since to allow the falsity of such propositions would be a kind of semantic error (playing the wrong language game). But this would seemingly reconstrue the the debate in anti-realist terms, by rephrasing the question in terms of whether this proposition can be doubted in the light of linguistic conventions. Put another way, Wittgenstein's use theory of meaning in effect makes the proposition come out as infallibly true simply based on the meanings of its terms, which is simply another way of saying that the proposition is analytic. This may all be true but it doesn't really confront the question of whether the proposition is infallibly justified in a way that makes it indefeasible. Wittgenstein himself seems to concede this point in On Certainty.   

2010-06-23
Rationalist Infallibilism
Reply to Glen Hoffmann

I think he does, but I think it's because he doesn't really understand himself why the 'hinges' are reliable - he can only talk in terms of practices, or moves that it would be madness to query.

I think there’s a much more obvious way of thinking about this, although it challenges some of our intuitions.  If there was a hinge that was necessary to playing the game of doing philosophy, then it would not be possible to speculate, philosophically, that it might be unreliable – or at least we would have to reject such a speculation.  If we need to be able to talk to do philosophy, then any philosophical theory inconsistent with ‘it is possible to talk’ must be false.  I think, in fact, that ‘Is it possible to talk?’ must, absolutely, have only one answer or not be a question – but the argument is longer.

A hinge may be necessary to the playability of the game, but it is not epistemologically prior to it – this is the thing I think Wittgenstein couldn’t see.  Or maybe he would have regarded this problem as 'pathological'.  The possibility of the game can’t be seriously questioned (since to ask a question is to make a move in the game) so neither can its hinges – it’s a modus tollens, not a modus ponens.

We’re maybe a bit inclined to be diverted by the game metaphor, and to think that we could make up different games with different rules, or that the words and sentences we use really are just ‘tokens’.  But the metaphor can’t be unpacked in this way – I’m inclined to think it can’t be fully unpacked at all (for open question sorts of reason) – because this unpacking itself is not outside of the game.

And it’s a fundamentally semantic game.  If we try to point to a practice that underlies it, we have to give an account of this practice within the game (however minimally) and what the practice is, exactly, then becomes hostage to the way the game is played.  Wittgenstein generally talks as though this doesn’t matter – freely mixing talk of practices with semantic examples.

Kripke’s rule-following paradox fairly clearly demonstrates that we can’t deduce rule-following from behaviour.  He draws the obvious conclusion that we can’t deduce language use from behaviour either (since language use is rule based).  He then goes on to give a sort of sociological / Kripke-Wittgensteinian account of how we get round this, which I think begs too many questions ...

I think the kind of argument I outlined above is less messy:  however radical its conclusions, we can’t conclude from Kripke’s paradox that we can doubt whether we are really reading his book or that his book is about his paradox.  If we ask someone whether they are adding or quadding we can only doubt which rule they are following by also doubting whether they are honest and competent interlocutors – doubting, in fact, whether we are playing the same linguistic game.  This is not a doubt which can be entertained unambiguously in a game which is failing in unpredictable ways (since then we couldn’t be sure whether we had managed a proper statement of the doubt).

Where this goes is that ‘we can do science because there is a real world out there’ may turn out to be a hinge in the scientific language game, but the priority of the game over the hinge undoes its epistemological precedence.  ‘There is a real world out there’ turns out to be a sort of scientific theory, as do other metaphysical speculations of the same kind.  We can experiment with different ways of talking - accepting or rejecting the ‘reality’ statement - and we might indeed find that it’s very hard to keep the game going without accepting it, but it still wouldn’t work as an epistemological fundamental.  We’d be demonstrating its truth from the playability of the game, rather than vice versa.

And this doesn’t depend on definitions or analyticity – it is not analytically true that we can talk.  It is not part of the ‘definition’ of language that it is possible to use it in this way.  ‘We can talk’ is, from the point of view of articulable enquiry, a synthetic a priori statement.