Asserting "faith" to be a pretence of knowledge seems to me to have 3 issues:
First, asserting it to be a pretence suggests that it is known that either their claim is wrong, or that the claim is unknowable.
It is common for people to believe that certain things are true without being able to explain how they know those things are true. In other words, one can pretend to know things that one doesn't know, even in cases where the relevant facts are, in fact, true.
You are right, of course, that many pretences to knowledge concern things that are either not known (by anybody) to be true, or which are known (by other people) to be false. Then there are the cases of pretending to know something when you
actually know that you don't know the thing (i.e. you recognise that you cannot justify the claim you are making about your supposed knowledge).
And yes, there can be claims to knowledge about things that are unknowable.
I don't think you've pointed out any kind of problem, so far.
While this may be the position of the atheist (agnostic or otherwise) it may not be the position of the theist. The theist may not be able to explain to you how they know, let alone convince you, and they may not even be able to articulate it to themselves, but does that mean they are wrong, or that the claim is unknowable to them? How would you know that they don't actually know?
People who actually know things can explain how they know the things they know. They can provide
justification for their beliefs. ("Knowledge", as Yazata keeps reminding us, is
justified true belief.)
People can't just magically know that things are true (or false). If they know something, they should be able to give reasons or explanations of their knowledge. Capacity to articulate is a separate matter.
You ask: how can we tell when somebody doesn't actually know something? We can ask them to justify their claim. If they are unable to give an adequate account of how they came to knowledge, that certainly suggests to me that they might be pretending to know when they don't really know. Doesn't it suggest that to you?
At this point in the discussion, I should probably also distinguish between beliefs and knowledge, because people tend to confuse those two things as well.
When a person believes X to be true, it just means they have become convinced that X is true,
for whatever reason. If that reason amounts to a valid
justification for the belief, then we can reasonably conclude, in addition, that the person
knows X to be true. On the other hand, if the reason is not a valid justification for the belief, there is no knowledge, but the belief remains nonetheless. This is regardless of whether X is, in fact, true or false. Thus, people can believe in true things and they can believe in false things. They cannnot, however,
know false things, because they are no valid justifications for false things.
Second, asserting "pretence" seems to imply a deliberate act of dishonesty on their part.
One can lie to other people and/or one can lie to oneself. Either way, one is pretending.
Third, if you pretend to know something, as even an atheist can do, how is that "faith"?
It has to do with the attempt to justify the claim to others (or to yourself).
Consider statements like "I believe in God because I have faith in God" or "I believe that God is real because I have faith [that God is real]."
Here, 'faith' is used as the explanation for holding the
belief. As I said, people can become convinced of things for all kinds of reasons.
In the first example, I would say that the statement is mostly likely better explained the other way around: "I have faith in God because I believe in God". That is "I became convinced that God is real - somehow - and since I can't give good reasons for why I became convinced I'm going to use 'faith' as my excuse."
In the second example, 'faith' is a placeholder that is supposed to stand in for justification. It's essentially pretending that the speaker has a valid justification for believing that God is real, while making no attempt to give any actual justification.
Suppose that, as a athiest, I were to come to believe that 2+2=5, for some reason (to pick a somewhat silly illustrative example). If you were to ask me why I believe that, I might be able to give you a reason for my belief ("My grade 1 teacher told me that 2+2=5 and I believe she was right.") But, clearly, I can't give you a valid
justification for why 2+2=5.
If pressed hard, maybe I'd resort to "I have faith that 2+2=5." If I was feeling especially defensive, I might add "I can't explain to you exactly how I know that 2+2=5, let alone convince you that it's true, but does that mean I'm wrong? Maybe that claim is simply unknowable? My answer is therefore just as good as yours. Who are you to claim that I don't actually know?"
If pressed even harder, I might settle with "Look, we're just going to have to agree to differ on the whole question of whether 2+2=5 or 2+2=4. You have your view; I have mine. I have strong faith that 2+2=5. You're really being quite rude in pushing this matter. My faith is deeply personal and it's quite inappropriate you to even question me about this. What are you - some kind of stickler for science and proof? Nobody can actually know anything for sure, you know!"
Now, you might be content to leave me to my delusions and move on with your life. But what if I insist on preaching my faith? Suppose I go to some "science forum" somewhere and start a thread asserting "2+2=5! Skeptics be damned!" I stop merely saying that "I believe that 2+2=5" and start saying, instead, that "I know for sure that 2+2=5". The first reply to my thread is "How do you know?" and my reply to that question is "You've just got to have faith, man! Maybe you just don't have the innate number sense that God gave me. Maybe you'll never get it. But it's true, regardless of what you believe. My faith tells me so!"
Does this sound at all familiar?
Faith is surely far more than any claim of knowledge, is it not?
It's an attempt to justify a claim to knowledge, in the circumstance in which one cannot provide any valid justification based on evidence or reasoning.
The assertion that "2+2=5" is a knowledge claim. Faith is an excuse one might give for being unable to provide adequate justification for that claim. When one pretends to have the knowledge and one does not actually have the knowledge, you have a faith. It can be a faith that you honestly believe in yourself, or just a faith you use to pull the wool over other people's eyes. Either way, the key is the pretence to knowledge that you don't actually have.
If an atheist "pretends to know" that God exists... is that religious faith?
Maybe. But your example doesn't really work since, by definition, an atheist who deludes himself that God exists is no longer an atheist.
Or does faith actually mean something else, imply something else, go well beyond any such claim of knowledge?
What do you suggest?
Defining "faith" as a pretence seems to be a way whereby atheists once again tell theists that they are wrong to have faith, that they are being deliberately dishonest in claiming as knowledge that which the atheist doesn't/can't.
Are you saying it
isn't wrong to have faith, in the sense of pretending to know things you don't know? Remember, I was careful to distinguish the usage of 'faith' to refer to matters of trust, based on actual evidence.
Let me hear the reasons why you think it's good and right to have faith, then.
As for the dishonesty thing, they
are being dishonest. In some cases it is deliberate dishonesty in communication with other people. In other cases, it might merely be self-delusion.
While an atheist might well think that about theists, I don't find that particularly useful in understanding what "faith" means for an actual theist who might use that term.
What do you think actual theists mean? Are you an actual theist with personal experience in this area?
So maybe we shouldn't be telling theists what
they mean by the term.
I'm all ears. Theists, please tell me what you mean.
(I might also mention that I've been on this particular merry go round with theists before. I fully expect that somebody will post the bible verse that talks about faith being evidence of things unseen, which just tends to confirm the pretending thing. Faith is the reason you give when you don't have evidence.)