Some sort of discussion of case would be most welcome in a "Tips and Notes" section. I realize the Polish group has an aversion to "cluttering up" the feed in some way, but a simple introduction to the new case as it comes along would not do that. The Turkish course does an admirable job, for example, and I believe the Ukrainian does rather well too. If it can be done for Ukrainian, surely it can be done for Polish. Of course, I understand if it is simply not up in beta and will be added later.
Ją is accusative and jej is genitive.
Genitive (jej) is used:
- to imply possession
- with units or amounts
- after certain prepositions such as dla, do, od.
- for the direct object in a negative sentence (only if the positive sentence would use the accusative!):
- indicates the direct object of the sentence
- is used with some prepositions to indicate a motion/change (exception: the preposition "w" (in) takes the locative when indicating a state/condition, but to imply change you must use the preposition "do" + genitive)
If you'd like to say "I don't like her" you would say "Nie lubię jej" (negative). But "I like her" is "Lubię ją".
"for the direct object in a negative sentence (only if the positive sentence would use the accusative!)"
So, in a negative sentence, all accusatives change to genitives, or am I getting it wrong? This is very unnatural to me, in Czech, there is no such change and I keep having troubles with this. :(
You also use the genitive case, 'jej', for possession. So "mam jej psa" means "I have her dog". The accusative case, 'ją' is not possessive, so it wouldn't make sense to say "mam ją psa". In English we don't differentiate between possessive and non-possessive 'her', but in Polish they are different words.
Just like in English you can't say "I like she" because that's a wrong case (there aren't much remnants of cases in English, but this is one), you can't say "Lubię ona" because that's also the wrong case. The verb "lubić" (to like) takes a direct object in Accusative, and the Accusative form of "ona" is "ją".
Whatever 'translation guide' you use (Google Translate), never assume that it understands grammar.