If it was you (formal), sie would be capitalized as "Sie", and the verb would be conjugated as third person plural to read "schwimmen". If sie is minuscule as "sie" and the verb ends in -en then "sie" is "they". For example:
Ich schwimme und Sie schwimmen = I swim and you swim
Ich schwimme und sie schwimmen = I swim and they swim
Ich schwimme und sie schwimmt = I swim and she swims
If the sentence was reversed you would need context for you/they.
Sie schwimmen und ich schwimme = You/They swim and I swim
Sie schwimmen und ich schwimme = They/You swim and I swim
Sie schwimmt und ich schwimme = She swims and I swim
Here's the verb "schwimmen" conjugated to show all endings:
Hope that helps!
So what if it was 'I swim backwards and she is swimming forwards'?
That also sounds unnatural to me.
Under what circumstances would you say that sentence?
It's easy to invent hypothetical sentences such as "I eat green lightbulbs every elephant", which are grammatical but don't make much sense.
Obviously there are some people who DO think it makes sense else we wouldn't have suggested it.
'so how are you getting the injured dolphin to the shore?' 'well, I swim backwards and pull, and [/whilst] she is swimming forwards'.
I take exception to your 'example'. Having spoken English, in England for half a century, I would hope that I actually make more sense than that. I wasn't plucking an example out of thin air for comic effect.
I put: "I am swimming and she swims" which convey two different clauses connected by a conjunction, each conveying -possibly, a different subtlety in the translation, which would of course depend on the wider context of the original, basically; however, I have gleaned this: that this could be a perfectly logical and correct translation.
I was actually testing the veracity of Duo's statements on the present tense in German. Please comment, as I may be missing something!
Judging from the discussion I don't really think you're missing anything. That was my logic as well, but I think they're just stressing tense agreement for some reason. I don't really understand why, if the tenses are the same it seems a lot more natural to just use one verb, but whatever. Not the most artificial sentence I've encountered here yet.
so when do you know if someone is saying 'I swim and she swims' instead of 'I am swimming and she is swimming'
In English, we generally use the present simple tense (e.g. "I swim") to talk about repeated or habitual actions ("I swim in the sea every Tuesday", for example), and we use the present continuous tense (e.g. "I am swimming") for an action that is taking place right now.
So if you just asked someone Was machst du jeden Dienstag? "What do you do every Tuesday?" and they reply, Ich schwimme, then you know that in English they would have said, "I swim."
On the other hand, if you ask someone, Was machst du gerade? "What are you doing right now?" and they answer Ich schwimme., then you know that in English they would have said "I am swimming."
The context (are you talking about repeated or habitual actions, or about something happening now) will tell you which translation is appropriate.
Without context -- as with individual sentences on Duolingo -- both translations will be accepted because you cannot tell whether you're talking about habitual actions or something taking place now.
i want to know what word to use to say 'I swim and she swims'
You would say, Ich schwimme und sie schwimmt.
So the lady this person is talking about must have a name, right? And she can say she's swimming herself. Is Duo just not creative enough to come up with names, or...?