"She has to wear glasses, because her eyes are weak."
Translation:Ŝi devas porti okulvitrojn, ĉar ŝiaj okuloj estas malfortaj.
It says I have a typo in my answer when I used siaj instead of ŝiaj for the second sentence bit, if that makes any sense. Could someone explain why you wouldn use siaj there?
Because "siaj" is refering to the nearest subject which in this case is "her eyes". But we are not talking about "her eyes' eyes" but about "her eyes".
"si" and its variants can never be part of the subject.
So if you wanted to say "She has to wear glasses, because she has weak eyes" you could say (in fact, would have to say) "Ŝi devas porti okulvitrojn, ĉar si havas okuloj malfortaj". Cxu ne?
I felt the explanation from Lernu was excellent for "si." However, when I came back to the example, I would interpret the sentence to be that she has to wear glasses because another woman's eyes are weak. The subject is neither the speaker nor the person being spoken to. Therefore, the second use of a pronoun must be a form of "si" so as to refer to the original subject... At least that's how I read it. My interpretation does not match the answer so I have a gap in my understanding. Any suggestions?
I got my translation wrong, because I used "bezonas" instead of "devas". After looking up the difference between the two, this is my mnemonic for keeping them straight: "bezoNi" is followed by a Noun, and "deVi" is followed by a Verb. So, for example, "Mi bezonas la libron; mi devas legi la libron."