The whole point of non-veridicality, if you like, is that there was a seeming that led you to believe something that wasn't so. But if what 'was so' was merely the seeming, this possibility seems to become incoherent. Sellars seems to want to say that this makes veridicality incoherent too, but I'm not sure what leads him to think this. — The Great Whatever
Okay, I'm gonna conjecture a little hypothetical that might illustrate Sellars' intuition on this matter. I'm gonna ramble a little, but I'm still in the "clear the area" phase here. Let me see what I can do here...
Suppose I make this claim: "I experienced a red triangle." Where is the self-verifying experience here? The experience of the red triangle is not self-verifying, since I very well could have seemed to see a red triangle even if there wasn't one (bad lighting or whatever, to use one of Sellars' examples). You could say that it's not the experience, but the
claim, "I experienced a red triangle," that is self-verifying, but that claim is grounded on my experience of
remembering a former a experience.
But that isn't being completely charitable to what you've put forth (also with deference to your point about delusion/dream/linguistic skepticism not being relevant here). Let's try and push it a little further:
while having the experience of seeing a red triangle, I say, "I seem to see a red triangle right now." You're saying I can't be wrong with that, yeah? Provided that the claim I'm making is totally grounded in
just that experience, and nothing else, then I can't be wrong.
I can't think of a problem with this offhand, so let me fiddle with it a little.
What would it take for me to be wrong here? I would need to have experience B, and infer something
false about B, with only B as grounds for my claim. Obviously, I can lie about it, but I take it as implicit here that it's self-verifying for me only. I guess the only way out for Sellars here is to ask for an account of what it means for a claim to be grounded in an experience. Perhaps he could say that there is something a little fishy about saying, "For any experience I have, it is self-evident for me that I am having that experience." Does one have an experience of self-evidence here? Or is this more of a logical thing, inferred from
what it means to have an experience?