Objectivist epistemology is the only epistemology that is worth a shit to me, i.e., in that any attempt to refute it necessarily ends up pre-supposing one of its precepts, ergo, it cannot be refuted, ergo, it is the only epistemology to bother with.
"She held that objective identification of the values of attributes of existents is obtained by measurement, broadly defined as procedures whose perceptual component, the comparison of the attribute's value to a standard, is so simple that an error in the resulting identification is not possible given a focused mind."
Regarding skepticism:
Hyper-bolic skepticism is self-defeating in that if you go around saying nothing can be established then neither you (your own existence) or the statements you are making can be established either. It is right up there with solipsism, i.e., it deserves no serious consideration. Nobody acts on a basis of solipsism or hyperbolic skepticism.
Maybe I was ambiguous. I was referring to 'error skepticism', and 'regress skepticism' rather error and skepticism as distinct entities. But your latter explanation answers my query; I am, however, unimpressed with that response.
To summarise: (1) skepticism is self defeatist, and (2) skepticism offers no ethical foundation. I'll refute each in turn.
(1):
Skepticism is not a proposal, i.e., "Knowledge doesn't exist." for that would be contradictory. Skepticism can be seen, within the Western tradition, as the philosopher's conscience. It asks: "If we prescribe to 'X' can we prescribe to 'Y'". Skeptics posit hypotheticals, not absolutes.
Consider the hard skeptic, he holds nothing - not even that nothing can be known. It's a dark room, but that metaphor can only get us so far because the skeptic can't even know that the room's dark. Skeptic's arguments go thusly, "I cannot run arguments in my metaphysic; however, I see you have a different metaphysical system and I see that within yours argument 'X' would be possible meaning the system collapses in on itself".
In that way skepticism is not contradictory, if you'd like to hear the skeptic's arguments (that run in your metaphysic) ask me to elaborate.
(2):
There's no logical bridge between what-is and what-ought; your metaphysic does not change your ethic; for example,
(1) Humans are egoists. (C) We ought to make egoist choices.
That doesn't follow; we'd need another proposition, namely: (2) The right thing to do is be true to ourselves. So now we have two distinct propositions (1), which is metaphysical, and (2), which is ethical. We see that any ethical conclusion must admit an ethical proposition. But now we have to support prop. (2), which can only be done using another ethical prop., a la, infinity.
Conclusion: there is no bridge between is and ought. (G.E.Moore)
All that is to say, nobody can act on the basis of a metaphysic.
Regarding 1), I would be certainly interested in what X can be shown to be true within Objectivism such that its establishment would undermine the system or cause a contradiction. As it is based on the Law of Identity I think one would be hard pressed to find an X that poses a problem, but hey, I'm all ears! :-)
Regarding the bridge between what-is --> what-ought. Certainly a hard problem prima facia. I'm not a trained philosopher, but I would say that, starting with "(A) != (!A)", one can say A "ought" to do action x if x preserves or enhances A's identity, that is to say, A's existence. So a black hole "ought" to accrete matter, because that is what black holes do, and accreting matter preserves and enhances the black hole's identity as a black hole, that is to say, it's existence, since, for Rand, identity is tantamount to existence. So man "ought" to be selfish because man IS by identity a selfish being. Acting selfishly preserves an individual's identity as a selfish being, i.e., preserves that individual's very existence. To "live for others" is to lose one's identity, and by declension, one's existence. "What-ought" it seems to me can have no meaning apart from the preservation of its subject or its actor. I "ought" to do that which preserves my genes, just like a black hole "ought" to accrue matter. There is no "ought" it seems to me divorced from preservation of existence, or preservation of identity. Thus:
1) Man is by identity selfish. 2) Man does not exist without his identity. 3) Man does not exist outside being selfish. 4) There is not "what-ought" beyond "what is needed to preserve existence of the actor, for all other meanings are subjective. 5) Man ought to preserve his existence. 6) By 2) existence is identity, so man "ought" to be selfish.
Admittedly a tough one, but that is my "stab" at it for the moment, ha!
Again, I would be interested in what X could be proved true within Objectivism such that Objectivism becomes inconsistent. :-)