"She knew that the carpet is dirty."

Translation: Ona wiedziała, że dywan jest brudny.

[Arnoldpitt]

Is this another example where not only the ending but the stem changes in the imperfect?

[alik1989]

Wiedzieć doesn't have a perfective stem, and I don't understand what you mean by "stem changes in the imperfect".

The past conjugation is irregular. There is an -ie- <-> -ia- alternation in the plural.

I think wiktionary will answer most of your verb-related questions.

[2nail]

How does she know that the carpet is dirty. I can understand her knowing it was dirty. Unless she has a gift of seeing into the future.?

[domnelson]

Because it was dirty then and it's still dirty now...

[2nail]

How did she know it is dirty. I have rephrased my question to match the original sentence. Therefore, the sentence I have written is equally incorrect in my opinion

[SunGalaxia]

That's not really grammatical in English though.

[dmkusner]

Would 'znała' work here instead of 'wiedziała'?

[alik1989]

No, znać must always take a direct object.

[Gigio72860]

Doesn't Polish have any sort of "consecutio temporum" ? Shall the sentence be rather "Ona wiedziała że dywan był/byłby brudny" ? Dzięki z góry. Z okazji... Wesołych Świąt!

[Jellei]

No, no sequence of tenses. At the moment we're talking about, the sentence "dywan jest brudny" was true in Present Tense. I guess we can assume that it's still dirty right now. "był brudny" makes sense (literally as "was dirty" - I guess it probably isn't dirty now), but "byłby brudny" is conditional, "would be dirty"- I guess maybe "would be dirty if we didn't hire a company to clean it"?

Wesołych Świąt! A bit too late, but... :D

[Musicalantonio]

It doesn't really sound right to me with "is" in English.

[JohnWinski]

Is znala the same meaning of wiedziala?

[Jellei]

No, "znać" takes a direct object (kinda like 'being familiar with something'), "wiedzieć" does not. "znała" doesn't work here.

"Ona znała tego mężczyznę" (She knew that man) is the right usage of "znała".