TSZ commenter walto published a paper this year in the Journal of Philosophy entitled Epistemic Closure, Home Truths, and Easy Philosophy. Unfortunately, the paper isn’t free — if you want to read it, you’ll either need to pay for it yourself or get it via institutional access (if you’re fortunate enough to have that.)
Regarding his paper, walto made the following remark to commenter Kantian Naturalist:
I don’t know if it counts as “a refutation”–but I think keiths’ version of skepticism requires the closure of knowledge under (known) entailment [which walto refers to as ‘CLR’ in his paper.] And I think that that premise can be shown to be false.
It’s a long story and you’ll have to get my paper to see how, but the abstract is available for a nickel.
I think walto hesitated to use the word “refutation” because he couldn’t rule out the possibility of arguments for skepticism that don’t rely on CLR. Any such arguments would be unaffected by the conclusion of walto’s paper, and skepticism might therefore remain standing. But any argument that did depend on CLR would be refuted if the conclusion of walto’s paper is correct and CLR is false.
We can (and likely will) discuss many of the technical details in the comments below, but unless I’m missing something fundamental, it appears to me to be surprisingly easy to show why walto’s paper doesn’t work as a refutation of CLR-based arguments for Cartesian skepticism.
His statement of the argument requires the following premise:
(ii) A competent reasoner sometimes knows such things as that she is sitting on a green chair.
That premise effectively amounts to a denial of Cartesian skepticism. So in order to use his argument agains Cartesian skepticism, walto first has to assume the falsehood of Cartesian skepticism just to get the argument off the ground.
The reasoning therefore ends up being circular:
1) assume that Cartesian skepticism is false;
2) using that assumption, deploy the argument laid out in the paper and conclude that CLR is false;
3) use that conclusion — that CLR is false — to negate any argument that requires CLR to be true, including arguments for skepticism.
It looks hopelessly circular to me, but walto is unlikely to take this lying down. Stay tuned for a vigorous debate.