See also Question 997 .

Also, if I were to tie your hand behind your back and then ask you whether you can touch your nose with it, that would be a peculiar question. And something similar is going on when one's asked whether one can defend all one's principles of reasoning. The whole practice of defending something assumes that principles of reasoning are in place. In fact, a cogito -like situation is indeed present: a state of affairs holds (thinking, defending) which demands presuppositions (existing, acceptance of rules) that make a certain doubt (about existence, about logic) self-stultifying.

To answer your good question, one needs to distinguish between the role experience plays in the acquisition of knowledge and the role it plays in the justification of knowledge. You're absolutely right that without experience humans would not be able to develop cognitively; they would not be able to acquire knowledge of anything at all. So experience, like oxygen, is needed in order for us to become knowers. But to say that some proposition is known a priori is not in conflict with this claim. To say that some proposition is knowable a priori means that one's justification of the claim need make no reference to information obtained through the senses. We can justify Pythagoras' Theorem without any information provided by our sense organs (take a look at any proof of it and you'll see that this is so). Hence, it is knowable a priori – even though no one could have known it unless they had had the experiences needed in order for their minds to develop.

The truth of "There is at least one true statement" (*) follows logically from the claim that " S is a true statement" (**), where S is some particular statement. So if we could establish (**) without presupposing the truth of (*), we would have answered your first question affirmatively. Let S be the statement "There is a pen on my desk now." Observation tells me that S is true. It seems that I can know that S is true, i.e., that (**) is the case, without the need to assume that (*) is the case. Hence, I can establish the truth of (*) in a non-circular fashion.

There is an old story told about the famous mathematician X [insert favorite famous mathematician's name]. X had just claimed in class that some result was obvious when a student raised her hand and expressed some uncertainty. X looked puzzled, then sat down and began to think. Minutes, then hours, went by while X was deep in thought. The class period was just about over when X raised his head and triumphantly proclaimed: "Yes, I was right: it is obvious!" The joke here is related to what makes your question a little peculiar. You want a justification for some claim that is being advanced as obvious? Its being so advanced presumably indicates that the speaker believes it to be in less need of justification than any premises he might offer in an argument for its justification. Furthermore, if justification consists of an argument, then it must have premises (or starting assumptions) that are not themselves argued for. And the justification will fail to be persuasive if the hearer does...

Are you imagining a situation in which x is F and y is F, but x is G and y is not G? And then are you asking whether all things that are G might also be F? If so, I think the answer is Yes: let x be Fido, your dog, let y be Kitty, your cat, let F be the property of being a mammal and let G be the property of being a dog. Fido is a mammal, as is Kitty; Fido is also a dog, but Kitty isn't; and also, all dogs are mammals.

There is a grand history of such discussions. One wonderful place to start is with David Hume's Dialogues Concerning Natural Religion , a modernized version of which you can find on the Web here .

Can we really defend Socrates here though? (Note: It's early Saturday morning and this is relevant to present fearless wading into rough waters.) He says that he is "likely to be wiser" by virtue of not asserting that he knows something worthwhile. But isn't wisdom knowledge? Doesn't being wiser require knowing a little more? If so, then it seems that Socrates really is saying that he knows that he doesn't know anything worthwhile. (That's the knowledge that makes him just a tad wiser.) And now we're back to worrying whether Socrates' assertion is paradoxical. I can imagine two responses: (A) one might claim that one's failure to know anything worthwhile isn't itself a worthwhile thing to know (and so Socrates' claim to knowledge doesn't clash with what he claims to know, viz. that he knows nothing worthwhile). Or (B) one might hold that one could be wiser simply by failing to claim knowledge that one doesn't have (so we can make sense of Socrates' claim to being slightly...

No, at least not when taken literally. A necessarycondition for knowing some proposition is that one have good evidencefor that proposition. (What exactly that condition amounts to issomething you could spend the rest of your life inquiring into.) But ifone has good evidence for a proposition then it can't be that one'sprobably wrong, if what that means is that according to all theevidence at one's disposal the proposition's truth is unlikely. Ofcourse, someone who says this is more likely simply trying to warn us against being overly confident about our judgments. So understood, pointtaken.

If you believe your death spells your total annihilation then your death presents more than a problem of how to acquire knowledge: once you die, there will be no you around to know (or not to know) anything. Indeed, there won't be a you around to undergo non-existence so there won't be anything (for anyone) to know. Non-existence isn't a particular kind of state that presents challenges to our knowledge; your non-existence entails that you are no longer around to be in any state. If you think death is merely the end of your corporeal existence and that your soul survives, then I'm not sure what to say: for, like you, I don't know what souls are or how they acquire knowledge.