"My aunt was an author who wrote a long book."
Translation:Mia onklino estis verkisto kiu verkis longan libron.
Wouldn't it be better to say "verkisto ke verkis longan libron?" as in "author that wrote a long book?" It makes sense in english but it seems wrong in esperanto to me.
No, this confusion came up in German with "dass" vs "das".
"Ke" is that when it is used like follows:
I know that he can do it. (Mi scias, ke li povas fari ĝin)
While this sentence might look the same it is not. Your that is referring back to the subject or object of another sentence.
He is a person that knows it. (Li estas homo, tiu scias ĝin)
Since you could use who in these cases, then you use kiu en Esperanto.
See if you can get these right. 1.) La viro esperas, ? li vidos lian filinon.
2.) Tio estas la knabo, ? manĝis la kukon.
3.) Esperanto estas lingvo, ? estas tre bela kaj facila
4.) Mia patro scias, ? mi estas malinteligenta
5.) La instruistino malamas, ? sia kafo malvarmas.
Thank you, Dave! Shouldn't your example (2) start with "Tiu estas"? If not - why?
why is "mia onklino verkistis kiu verkis longan libron" incorrect? It seems a bit awkward-sounding, but it is a useful shortcut to "estis verkisto" that doesn't seem semantically ambiguous
I've read before that you have to be careful doing that with nouns, don't know why and it seems to be done more with adjectives. Eg Nokto malvarmas etc.
That would not be necessarily true. Contemporary authors often use computers rather than a pen and a paper. Also writing (or typing) is a secondary thing. Primary is to put words right, to draw the characters, to develop the plot, etc. You can "write" a book by dictating it to someone. In that case you'll be "verkisto", but not "skribisto".