"Finally, after twenty years he saw her again."
Translation:Konečně ji po dvaceti letech zase viděl.
"ji" is a clitic just like every short form pronoun (ho, mě, tě, se, etc.), clitics are placed in the second position. These are some of the possible variations (with difference on what is the new information being communicated and what is stressed):
Konečně ji po 20 letech zase viděl.
Konečně ji zase viděl po 20 letech.
Zase ji konečně viděl po 20 letech.
Viděl ji konečně zase po 20 letech.
Po 20 letech ji konečně zase viděl.
On ji konečně zase viděl po 20 letech.
That's only wrong because it has to be "letech". "Po" is one of the prepositions that means different things with different cases. So "po dvaceti letech" (locative) is "after 20 years", while "po dvacet let" (accusative) means "for twenty years" (duration) - (here the "po" is often omitted just like "for" can be omitted in these expressions), and that makes no sense "he finally saw her again for 20 years....?".
Otherwise, "Po 20 letech ji zase konečně viděl" sounds correct to me, although I would personally prefer saying "konečně" first. Like I said in my previous post - "Here are some of the possible variations", it would be a really long list to give you all correct solutions.
Wow, thank you! I had no idea that all those forms were clitics! That should help a lot!
To be honest, I had never heard of clitics before starting this course. In fact, I have had to learn an awful lot about the structure of language in general in order for this course to make sense.
I don't know if it's the same in other languages/countries, but in the UK, when I was at school, I don't remember any of this stuff being taught, and of course, as native speakers, we can speak our own language perfectly well without knowing most of this esoteric stuff.
I feel like I'm getting an intensive course in linguistics from Duo, as well as learning Czech. No wonder my brain hurts sometimes!?! :D
Most people pay no attention to grammar taught at primary school. It sounds silly to most of us when teachers try to explain our own language to us using complicated words and constructions, we see no purpose in it until we start learning another language - then it suddenly becomes useful.
It also depends on the two languages (the target language, and the language you're using to learn the target languages) -- some grammar stuff is shared between them (nouns, verbs, tenses...) while some features are unique to one of the two. For example, you don't really need the term "clitic" to understand English, as it pretty much only refers to contracted aux. verbs in "I've" or "we're", whereas it's quite important when trying to explain Czech syntax.