They are defined as being sure a statement is true beyond doubt.
At least orathaic knows what I'm trying to get across. I had thought Putin et al were merely refusing to accept my points but it now seems they actually didn't understand me. Sorry to have failed in that respect.
I will try another time to sum it up - Putin believes he can trust his senses and memory. From this believe he construes "knowledge." That is - if his senses and memory were trustworthy, he could be said to know several things, one of the most important being that it is likely that his senses are usually correct.
But all of that is founded on the idea that the senses and memory are usually trustworthy, which is a position you actually *don't* have any evidence for, it is just something you choose to believe on faith. Which is fine, I have the same believe. The difference between us is I acknowledge that it's a belief whereas you maintain knowledge.
The difference between knowledge and belief, one more time, is that belief is a viewpoint you realize could be false but you choose to hold the view anyway and live your life accordingly. Knowledge is instead something that there is no possibility could be false. Essentially, you have no choice whether or not to believe it, because it is just true. And once again I am saying that there is nothing like that. There are no things that just automatically true - *any* statement of fact (which is a claim about the real world) could potentially be incorrect.
To try to address your specific obsession with communication:
It seems you think that because we appear to be successfully communicating (dunno about that :P) that you can know that we are both real people using English and so on.
But as orathaic brought up - could I not just be an imaginary friend of yours? You could be having a delusion wherein this user named Thucydides who in fact does not exist at all is saying all these things. It could be that all the real posts in this thread are just you rebutting points no one made, and the rest of the community saying "putin who the hell are you talking to?" But you wouldn't know that because your eyes and memory are fooling you.
If you first of all believe that this situation is impossible, well then I guess where the issue is. But I think you would have to acknowledge that this type of thing is possible. I think what you have been saying is that it is possible but very unlikely.
However, again (whew), when you say "it is unlikely that my memory is wrong all the time," you have one piece of evidence for that - and one only - your memory itself.
I, personally, have 20 years of memories of me living in this world which has up till now appeared remarkably coherent and real. But, to use an example I've heard elsewhere, it is actually possible that God created me three seconds ago and gave me all these memories. So then I would actually be wrong that my memory is trustworthy.
Saying that the above situation is unlikely is only correct in that any situation of reality you can dream up is unlikely because it is so specific. The central requirement though is to also acknowledge that, just as unlikely, is the "real" world, and the normal explanation for everything. This worldview has no monopoly on truth or even likelihood.
You also use the following argument more than once:
But if my senses or memory were fooling me, I would very quickly realize it when I (eg) walk into a crowded street that I thought was empty, or, when I try to communicate with what I thought were your words but actually were not. You're basically saying - hey, if I was wrong about the real world, the real world would get through to me and say "hey, you've been wrong up to now!"
How exactly do you know that would happen? If your *entire* life has been a hallucination, why do you assume you would get into trouble in the next moment? Doesn't it make more sense that whatever has been making things seem coherent up till now will continue to do so? It is at least possible, and because of this, it is also possible that you are wrong about everything.
Seeing this, a skeptic says nothing is known where something that is known is defined as something that cannot be doubted. Once nothing is known, all facts that inform our decisions are actually beliefs (which require no evidence and are just personal decisions).
Orathaic, i think about two pages ago I had about 4 posts in a row, the first two being quite long. The one with headings on it is where I quote my own writing about the usefulness of skepticism.