"The girl is not eating a tomato."
Translation:Das Mädchen isst keine Tomate.
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'.
I think it is a rule to use keine whenever a noun with indefinite article is negated.
Like yaqo said, you will never say "[verb] ein [noun] nicht"; you will always say "[verb] kein [noun]".
You can use "nicht" you just have to pay attention to the word order. "Das Mädchen isst nicht eine Tomate" is correct
Yes I am very sure http://german.about.com/od/grammar/a/The-Position-Of-Nicht.htm
"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.
I am trying to understand where "nicht" comes and where comes "kein"....
"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