The overall plan ....

Here is a rough synopsis:

(1) For broadly Davidsonian reasons, as well as others, we can roughly identify our 'conceptual scheme' with the conversation we are presently engaged in, and since we identify other things as conversations only if we can translate them, we end up with, in a rather ragged way, only one conceptual scheme. If we think it might have inconsistencies, we can try to find them & eliminate them. We have no intelligible way of speculating about what kind of language game this process would result in, because we would need to be able to translate it into the language we use now in order to indulge this speculation; and this is something we cannot, by definition, do.

(2) Although synthetic a priori beliefs may be elusive, synthetic a priori statements are easy to construct, as we can make general statements about the possibility of language: 'We can speak' is either true or not a statement. We need to be able to make assertions, because to deny this is to make an assertion. If we can make assertions, then 'We can speak' has the corrollary 'We can tell the truth'.

(3) Generic theories of truth (of how to speak) are blocked by the open question argument. Statements that it isn't possible to know we're telling the truth are self-refuting. So we must be able to know we're telling the truth without being able to say why, in order for language to work: and since we can assert the latter a priori, the former must be the case.

(4) The structure of fundamental arguments now becomes recursive: we can never argue 'X must be true because it is a theorem of my theory of truth', and we certainly can't argue 'X must be true because it isn't possible to tell the truth with certainty'. The only alternative is the transcendental argument: 'X must be true or it would not be possible to tell the truth'.

(5) Since 'We can speak' is an empirical statement, it is possible to construct fundamental empirical arguments transcendentally: Either Empirical(X) is true or it is not possible to make empirical statements. This is the bridge from reason to the world.

(6) While it may be possible to construct a transcendental argument (as in 5) for the reliability of the senses, this would not rescue traditional sensory empiricist epistemology - it would show that the reliability of the senses depended upon the reliability of empirical statements, and not vice versa.

Some stages obviously need elucidation (!) and there are lots of interesting consequences and further developments...

But the main elements are all here.

Another take on the Open Question Argument?

Suppose a group of interlocutors agreed on an articulated theory of truth for the language they were using: they would also, then, have to be considered to share an interpretation of the theory. And this is something they cannot articulate within the language - they can only point to the continuation of the conversation.

Another way of putting this: Sharing an articulated theory of truth is also sharing an interpretation of such a theory, and our only grounds for saying that we share an interpretation are the same grounds we have for saying we share a tacit theory of truth - that we can can continue talking to one another. And within the language game we are using to converse, we know this a priori. If the interpretations diverge, the game breaks down - and we don't even have anything with which to say that it has broken down, far less discuss our varying interpretations.

(We do, obviously, discuss varying interpretations of some linguistic moves - but only within a shared framework of truth-telling.)