Hesekiah made an important concession on his blog:
I agree. I see we have something in common.
I don't mean "important concession" in the sense of "dumb pre-supper has admitted something he shouldn't have. Hah hah hah!" but that it is a concession that might allow us to have a dialogue; something that the standard pre-suppositionalist position (tactic?) of denying any common ground with an opponent prevents.
Now to construct a mutually convincing argument in favour of any proposition would require a whole heap of common ground between us. As “proof” sets up an infinite regress to mutually “prove” a proposition would require infinite common ground: which is impossible.
We need very little common ground though to find out that things are not correct. That allows us to argue not in a standard manner from common ground to agreement of how things are but from common ground to agreement of what is not. It enables us to argue abductively:
Schemata of an abductive argument
2. If A then E1
3. If B then E1
4. If C then E1
7. E2 then not B and not C
8. Not (E2 then not A)
9. Thus A
Step 1 is our evidence. In steps 2 to 4 we try to explain E. In step 5 we give up trying to come up with more explanations. In step 6 we introduce more evidence and note that it contradicts B and C (step 7), but not A (step 8) leaving us to conclude A.
It is crucial that we interpret step 5 correctly. If we interpret it as saying there is no other explanation than A, B or C then it is almost certainly false. At the very least we have no idea whether it is true or not. If we interpret it as “we can’t, at the moment, think of any other explanation” then it is true and it is this that is carried to the conclusion. The argument establishes that A is the only thing we can think of that is not evidently junk.
The argument is valid. Not only is it valid, it's secure. The evidence, obviously, is …well... that’s the evidence, that's the common ground. Steps 2 to 4 are just analysis of the meanings of theories A to C, as are steps 7 and 8. The argument also ought to be persuasive: what are you going to do, accept the theories that are evident junk or the one that at least stands up to scrutiny?
So it’s valid, it’s secure, you ought to accept A.
But A is not necessarily true, it’s just the best we have available at the moment. A then is not proven. Where A is not true, “A” is not “knowledge”: but you should still accept A (everything else you can think of is evidently junk). It’s not proven, it’s not knowledge but you should still accept it: neither knowledge nor proof are necessary.
And it’s a valid argument that is not circular. The conclusion, A, appears nowhere in the premises. We have not assumed A to establish A.
Now when we say it’s secure, it’s temporarily secure:
New evidence may come forward, E3, that also contradicts A.
Of course we may still prefer A to B or C as A, at least, copes with E1 and E2; which is better than either B or C do. (Newtonian Mechanics is false, as shown by relativistic effects (the Newtonian mechanics “E3”) but we still use it for everyday tasks where it does work (the “E1” and “E2”)
Or we, or someone else, might extend step 5.
“What about D?” says someone. “Ooh, we hadn’t thought of that.
Mind you this just changes the conclusion from “A” to “A or D”. What really works as a refutation is providing both falsification of the existing theory (E3) and a new theory (D) which explains all the evidence.
What doesn’t remove the security is questioning the basis for A. There is no “basis”: the evidence, E1 and E2, does not “support” A in any inductive or probabilistic sense.
Asking for a basis for anything is a non-argument: show where it’s wrong and what’s better. The same goes for the entire style of argument. I do not need to show a “basis” for thinking it true; it’s the best position I can manage, if you have a better one show it to me (D) and show how it is better (E3). I don’t need to show a “basis” for logic: it’s the best position I can manage, if you have a better one show it to me (D) and show how it is better (E3). I don’t need a basis for either of those two statements, I just think: they're the best positions I can manage, if you have a better one show it to me (D) and show how it is better (E3)
The Transcendental Argument for God (TAG)
Above is a long (though not as long as I could make it) demonstration of an alternative theory to the "pre-suppositions" underpinning TAG. The above is to TAG as D is to the model abductive argument: we don't need proof, certainty, or "knowledge"; this is how we can do things.
Have I got an E3 for TAG? Why yes. You see TAG is in much the same form as an abductive argument, a form that does not show that its conclusion is true, but that others are false. But the "evidence" it takes is that an abductive argument isn't good enough, you must establish proof, certainty and "knowledge". Now if an abductive argument is not good enough then TAG, which is an abductive argument, is not good enough. TAG argues for it's own rejection.