"I do not know who he is."
Translation:Mi ne scias, kiu li estas.
Surely this is dependant on context, whether one uses scias or konas. Scias would mean that I know him, but not from personal experience, whereas konas means that I know him personally, from personal experience, ĉu ne?
No, you're not actually talking about him, but about your knowledge about him.
Or more linguistically speaking: The object of the sentence is not 'li' but the whole subordinate clauses. C.f.:
"Mi (ne) konas lin." or "Mi (ne) scias, kiu li estas.
In a previous question, it asked to translate "you don't know what to say" and accepted the translation "vi ne scias kion diri".
Why is it "kiu li estas" in this sentence instead of "kiun li estas"?
I thought if the kio/kiu are the object of "scias", then they should be in the accusative case. One works, and the other doesn't. Why not?
The object of "scias" are the whole subordinate clauses "kiu li estas" and "kion diri" respectively.
In the clause "kiu li estas" 'kiu' and 'li' are both nominative since they are linked via the copula 'estas'. In "kion diri" 'kion' is in the accusative because it is the object of 'diri'.
I hope that explanation helps!?
Thanks Tareberon. I don't know what a "nominative" or "copula" are, but I think I've got my answer when you said that "Kion" is the object of "diri".
Generally speaking, the nominative is the case of the subject, and the accusative is the case of the direct object.
In Esperanto the nominative isn't marked, while the accusative is marked with an -n
Nominative: viro, knabo, patroj, domoj
Accusative: viron, knabon, patrojn, domojn
Copula comes from Latin and means 'tie' or 'belt'. It's called that, because it ties two nouns (or a noun and an adjective) together. In Esperanto the verb 'estas' ist the copula.
Long story short: Never use the accusative with the verb 'estas'.
Is the comma obligatory here? I see sentences with dependent clauses like this without commas all the time in other languages but only exclusively written like this in Esperanto.
As far as I can tell, it is like in German: All clauses are separated with commas:
" Mi ne scias, kiu li estas."
"Ich weiß nicht, wer er ist."