Okay, you've asked a difficult question and there's a lot to unpack here.
However, I think it does express the meaning I intend: I didn't know that in the past, yes, but now one person tells me that, and I say: I haven't known that up to now/up until now.
I didn't know that in the past, yes. but the situation has changed in the present, the situation has changed just now! The past fact or state connects to the present event: it has changed just now!
Yes, I follow your thinking. Well, if you really mean that, then
I haven't known that says what you mean. The problem is that for us it's not the right thing to say in this particular situation.
In this particular situation, you're really talking about the past. You're saying that before emsr2d2 told you this new information, you were in a state of ignorance about it, so the past tense is the tense to choose:
I didn't know that = until you just told me. I think your choice of the 'distant' word
that, as opposed to
this, also confirms that you're thinking about the past and not the present.
Having thought it over I think that I can't use the present perfect with 'know' there is not so much a problem of the past simple or the present perfect simple (i.e. of the tenses) but that the meaning of the verb 'know' changes if or when you use the present perfect with 'know'. Then It tells you what you have seen, heard or experienced or not seen, heard or experienced as in sentences like I've never known it to snow in July, or She has known what it is like to be poor?
Some of this is insightful. You're right to be careful to consider differences in meaning of the verb
know, which is a very tricky verb. In the cases of
I haven't known Peter for long, or
I haven't known it to snow in July, you have a quite different sense of the verb, yes.
That meaning doesn't fit the situation I have described above.
Right.
Nevertheless, it puzzles me: is this a confirmation or a ban on using the present perfect there?
It's a suggestion that in this situation, with this particular utterance, you say
I didn't know that because you mean 'I didn't know that
until you just told me'.
May be in the situation above I can say I've been ignorant of that up to now/up until now or I haven't had the faintest idea of that up to now.
Yes, you can. And if you really do want to talk about the present result of your recent knowledge, you can set the perfect aspect more clearly by using
never instead of
not and
this instead of
that:
I've never known this until now.
From my point of view as a teacher, I can see one more complicating factor here, which is that you're not a native speaker, and moreover, you're a German-speaking non-native speaker. That makes
I haven't known that sound to us like a conspicuous learner error. Germans typically have little trouble with English grammar, but perhaps the single most obvious area of verb grammar misuse that gives a German away is precisely the overuse of the present perfect in cases where we natives would use the past simple. I'm guessing that part of the problem for you here is that you have in mind a thought that
would be expressed with the German equivalent of the present perfect.
