"The girl is not eating a tomato."

Translation: Das Mädchen isst keine Tomate.

[Cleitaro]

Why "Das Mädchen isst die Tomate nicht" is not good?

[Menschenkind]

Because 'a' is indefinite and 'die' is definite. Your translation would imply a special, present tomato. The english sentence doesn't though, so you use the indefinite 'keine'.

[vanchy]

and why "das Mädchen isst eine Tomate nicht" isn't correct? thnx

[yaliyev]

I think it is a rule to use keine whenever a noun with indefinite article is negated.

[LB_StorM]

Like yaqo said, you will never say "[verb] ein [noun] nicht"; you will always say "[verb] kein [noun]".

http://german.about.com/od/grammar/a/German-Negation.htm

[KendallHolm]

You can use "nicht" you just have to pay attention to the word order. "Das Mädchen isst nicht eine Tomate" is correct

[yaliyev]

Are you sure about this? What do native speakers think?

[KendallHolm]

Yes I am very sure http://german.about.com/od/grammar/a/The-Position-Of-Nicht.htm

[espanalee]

What's the difference between kein、keine、 keinen？I am totally confused.

[yaliyev]

"kein" is inflected as "ein". If you negate a noun with "ein" then use "kein". Similarly, if you negate noun with "eine" or "einen" then use "keine" or "keinen", respectively.

[espanalee]

Oh,I see ,thank u .

[yizhu.wang]

Then how to say “the girl does't eat tomato”? Like she never eats tomato

[Sagher]

I am trying to understand where "nicht" comes and where comes "kein"....
For example:
"Ich esse nicht"
"Nicht" is with "essen" which is an infinite verb and not anything we can see or touch...
But in this example: " ich esse keine tomate"
"Keine" is related to "tomate" not "essen". And tomato is a thing we can touch, see, etc...
Is my judgement right? Is there any rule like this? Plz confirm