"Він знає, а ми не знаємо."

Translation: He knows and we do not know.

[wATB7]

It seems incorrect to you "and" for contrasting verbs. "But" may be more fitting here than "and".

[sagitta145]

Both are accepted

[wATB7]

*use

[ChristinaSuko]

I agree with you.

[Ludwig_Sakata]

Is there always a comma before "a"?
Just like this one?

[deniko]

Yep!

[Tielbert]

The comma always precedes the new clause

[BarryLord1]

"You know but we don't know" is correct but not accepted. "We do not know" is stilted English. It's starting to get on my nerves that I have to write English that only a foreigner would use.