The naturalized epistemologist and the old school foundational internalist may be stuck in an argument of "nuh-uh" vs. "yes-huh":
(1) We (as philosophers) believe certain rules of deduction to be valid (eg modus ponens) but not others (eg modus morons--the fallacy of affirming the consequent).
(2) We can show through meta-theory why this is so, but even the meta-theory will implicitly depend on our use of the valid rules.
(3) The internalist will account for this by claiming that we can know certain things a priori.
(4) The naturalist will account for this by claiming that we are (as DePoe pointed out) 'hard-wired' to reason in such a way.
Now, for those of you in McGrew's Epistemology class, yesterday you witnessed his argument against 4. For those who were not, or have forgot, here is it's basic form:
What evidence is there to believe that this hard-wiring occurs? As those of us who have taught an introductory logic course will attest, students often commit modus morons fallacies, and have trouble seeing the validity of rules that are, to the trained eye, clearly truth-preserving. Evidence for hard-wiring is minimal at best.
It doesn't obviously follow from the fact that people have trouble grasping the formal rules of logic, that they do not view the world through logical glasses. Even if someone might mistakenly use modus morons in a formal proof, there is a good chance that they will not accept the following argument:
(5) If I'm George W. Bush then I have skin.
(6) I have skin.
(7) I'm George W. Bush.
An analogous occurence might occur when students make the jump from numerical arithmetic to algebraic variable arithmetic, that is, a young student who could easily perform (8) might have difficulty performing (9).
(8) 23 + 36 = ?
(9) 23 + x = 59
Is this proof that we do not see the world quantitatively?
Also, is an evidential argument against hard-wiring a proof for the a priori? Doesn't it make equal trouble for the foundational internalist that students have difficulty seeing the validity of these supposedly foundational beliefs? How can they build up from the foundations without having rules like modus ponens? Certainly my dog didn't work out the logic of MP before making the inference from:
(10) If there is a sound of a can opening, food is placed in my dish shortly thereafter.
(11) There is a sound of a can opening.
(12) Food will be placed in my dish shortly.
I'm not sure what I'm supposing this post to have demonstrated, other than that there might simply be a question-begging theoretical dispute between the Quinean and the Cartesian.
"Those beliefs are hard-wired."
"Nuh-uh, they're a priori."
Somebody show me the arguments and prove me wrong!!